Declare PAuth for Secure world as experimental

Declare ENABLE_PAUTH and CTX_INCLUDE_PAUTH_REGS
build options as experimental.
Pointer Authentication is enabled for Non-secure world
irrespective of the value of these build flags if the
CPU supports it.
The patch also fixes the description of fiptool 'help' command.

Change-Id: I46de3228fbcce774a2624cd387798680d8504c38
Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>
diff --git a/Makefile b/Makefile
index 8656da5..11d0d7a 100644
--- a/Makefile
+++ b/Makefile
@@ -478,6 +478,12 @@
 ifeq ($(ENABLE_PAUTH),1)
     ifeq ($(CTX_INCLUDE_PAUTH_REGS),0)
         $(error ENABLE_PAUTH=1 requires CTX_INCLUDE_PAUTH_REGS=1)
+    else
+        $(info ENABLE_PAUTH and CTX_INCLUDE_PAUTH_REGS are experimental features)
+    endif
+else
+    ifeq ($(CTX_INCLUDE_PAUTH_REGS),1)
+        $(info CTX_INCLUDE_PAUTH_REGS is an experimental feature)
     endif
 endif