[sw/dif] CSRNG Initial Implementation

This commits adds the following dif_csrng functions:

*   `dif_csrng_init()`
*   `dif_csrng_configure()`
*   `dif_csrng_get_cmd_interface()`
*   `dif_csrng_get_output_status()`

Added unittest and smoketest boilerplate.

Signed-off-by: Miguel Osorio <miguelosorio@google.com>
diff --git a/test/systemtest/config.py b/test/systemtest/config.py
index 14ddfc0..a5b9646 100644
--- a/test/systemtest/config.py
+++ b/test/systemtest/config.py
@@ -70,6 +70,9 @@
         "name": "dif_clkmgr_smoketest",
     },
     {
+        "name": "dif_csrng_smoketest",
+    },
+    {
         "name": "dif_entropy_smoketest",
     },
     {