build: mark DICE_PROTECTION_ENVIRONMENT as an experimental feature

The DICE_PROTECTION_ENVIRONMENT support has been marked as experimental
since it has not incorporated into the threat model.

Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: Ic1ea4d59fd8a3fde7ce0404488a56e9d11bc1b85
diff --git a/Makefile b/Makefile
index 57e27ca..ad3ef7e 100644
--- a/Makefile
+++ b/Makefile
@@ -1017,6 +1017,10 @@
         $(info PSA_CRYPTO is an experimental feature)
 endif
 
+ifeq ($(DICE_PROTECTION_ENVIRONMENT),1)
+        $(info DICE_PROTECTION_ENVIRONMENT is an experimental feature)
+endif
+
 ################################################################################
 # Process platform overrideable behaviour
 ################################################################################