musca: Mark Musca targets as experimental

TF-M and PSA have experimental APIs. Musca targets must initialize the
tfm_ns_lock, via the experimental API tfm_ns_lock_init(), as part of
their ordinary initialization procedure. Therefore, Musca targets must
have experimental APIs present in order to function. Add the
experimental API feature to Musca targets by default to ease usability
of the Musca targets, rather than requiring all users and CI to manually
enable experimental APIs when using these targets.

targets/targets.json

@@ -4661,6 +4661,9 @@
             "ARM_SSG",
             "MUSCA_A1"
         ],
+        "features_add": [
+            "EXPERIMENTAL_API"
+        ],
         "forced_reset_timeout": 7,
         "release_versions": [
             "5"
@@ -4718,6 +4721,9 @@
             "ARM_SSG",
             "MUSCA_B1"
         ],
+        "features_add": [
+            "EXPERIMENTAL_API"
+        ],
         "forced_reset_timeout": 20,
         "release_versions": [
             "5"