[dv, doc] Replace all 'dv.plan' with testplan

This commit purges all instances of "DV plan" to make the documentation
nomenclature as described in our DV methodology consistent.

what we capture in the HJSon -> testplan
what we capture in the markdown doc -> DV document

Signed-off-by: Srikrishna Iyer <sriyer@google.com>
diff --git a/util/uvmdvgen/uvmdvgen.py b/util/uvmdvgen/uvmdvgen.py
index 4cb297d..64f67e5 100755
--- a/util/uvmdvgen/uvmdvgen.py
+++ b/util/uvmdvgen/uvmdvgen.py
@@ -107,7 +107,7 @@
         "--env-outdir",
         metavar="[hw/ip/<ip>]",
         help="""Path to place the full testbench code. It creates 3 directories
-        - dv, data, and doc. The DV plan and the testplan Hjson files are placed
+        - dv, data, and doc. The DV doc and the testplan Hjson files are placed
         in the doc and data directories respectively. These are to be merged
         into the IP's root directory (with the existing data and doc
         directories). Under dv, it creates 3 sub-directories - env, tb, and