[util] Fix docstrings and arg names in `util/make_new_dif.py`.

As part of an effort to clean up the `util/make_new_dif.py`
documentation, as described in #8142, this commit makes the docstrings
and command line argument names more descriptive.

Signed-off-by: Timothy Trippel <ttrippel@google.com>
diff --git a/util/make_new_dif.py b/util/make_new_dif.py
index d626c85..7d06753 100755
--- a/util/make_new_dif.py
+++ b/util/make_new_dif.py
@@ -5,16 +5,24 @@
 """make_new_dif.py is a script for instantiating templates needed to begin
 development on a new DIF.
 
-To instantiate the files for a new IP named my_ip, run the command
-$ util/make_new_dif.py --ip my_ip --peripheral "my peripheral"
-where "my peripheral" is a documentation-friendly name for your peripheral.
-Compare "pwrmgr" and "power manager".
+To instantiate the files for a new IP named ip_ctrl, run the command:
+
+$ util/make_new_dif.py --ip-name-snake "ip_ctrl" --ip-name-long "IP Controller"
+
+where "IP Controller" is a documentation-friendly name for the IP.
+For example, compare "pwrmgr" and "Power Manager".
 
 It will instantiate:
-- `sw/device/lib/dif/dif_template.h.tpl` as the DIF Header (into dif_<ip>.h).
+- `sw/device/lib/dif/dif_template.h.tpl` as the DIF Header boilerplate
+  (into `dif_<ip>.h`), which should be manually edited/enhanced.
 - `sw/device/lib/dif/templates/dif_autogen.h.tpl` as the autogenerated DIF
-   Header (into dif_<ip>_autogen.h).
-- `doc/project/sw_checklist.md.tpl` as the DIF Checklist (into dif_<ip>.md).
+  Header (into `dif_<ip>_autogen.h`).
+- `sw/device/lib/dif/templates/dif_autogen.c.tpl` as the autogenerated DIF
+  implementation (into `dif_<ip>_autogen.c`).
+- `sw/device/lib/dif/templates/dif_autogen_unittest.cc.tpl` as the
+  autogenerated DIF unit tests (into `dif_<ip>_autogen_unittest.cc`).
+- `doc/project/sw_checklist.md.tpl` as the DIF Checklist (into dif_<ip>.md),
+  which should be manually edited.
 
 See both templates for more information.
 
@@ -53,15 +61,16 @@
     parser.add_argument(
         "--mode",
         "-m",
-        choices=["single", "batch"],
-        default="single",
+        choices=["new", "regen"],
+        default="new",
         required=True,
-        help="mode to generate DIF code; use 'single' if no DIF code exists.")
-    parser.add_argument("--ip",
+        help="mode to generate DIF code. Use 'new' if no DIF code exists."
+        "Use 'rege' to regenerate all auto-generated DIFs for all IPs.")
+    parser.add_argument("--ip-name-snake",
                         "-i",
                         help="the short name of the IP, in snake_case.")
-    parser.add_argument("--peripheral",
-                        "-p",
+    parser.add_argument("--ip-name-long",
+                        "-l",
                         help="the documentation-friendly name of the IP.")
     parser.add_argument("--only",
                         choices=ALL_PARTS,
@@ -73,12 +82,12 @@
     # Parse CMD line args.
     ips = []
 
-    # Check for batch generation mode (used in CI check:
-    # ci/scripts/check-generated.sh")
-    if args.mode == "batch":
+    # Check for regeneration mode (used in CI check:
+    # ci/scripts/check-generated.sh)
+    if args.mode == "regen":
         if len(args.only) != 1 or args.only[0] != "autogen":
             raise RuntimeError(
-                "can only batch generate completely auto-generated code.")
+                "can only regenerate DIF code that is auto-generated.")
         # Create list of IPs to re-generate DIF code for.
         for autogen_src_filename in glob.iglob(
                 str(REPO_TOP / "sw/device/lib/dif/autogen/*.c")):
@@ -87,12 +96,11 @@
             # case snake mode (i.e., uart).
             ip_name_snake = Path(autogen_src_filename).stem[4:-8]
             # NOTE: ip.name_long_* not needed for auto-generated files which
-            # are the only files (re-)generated in batch mode.
+            # are the only files (re-)generated in regen mode.
             ips.append(Ip(ip_name_snake, "AUTOGEN"))
     else:
-        assert (
-            args.ip and args.peripheral and
-            "ERROR: must pass --ip and --peripheral options in 'single' mode.")
+        assert args.ip_name_snake and args.ip_name_long, \
+            "ERROR: pass --ip-name-snake and --ip-name-long when --mode=new."
         ips.append(Ip(args.ip, args.peripheral))
 
     # Default to generating all parts.