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/docs/firmware-design.rst b/docs/firmware-design.rst
index 52520ea..66b16fa 100644
--- a/docs/firmware-design.rst
+++ b/docs/firmware-design.rst
@@ -2565,11 +2565,16 @@
    must be set to 1. This will add all pointer authentication system registers
    to the context that is saved when doing a world switch.
 
-   The Trusted Firmware itself has support for pointer authentication at runtime
+   The TF-A itself has support for pointer authentication at runtime
    that can be enabled by setting both options ``ENABLE_PAUTH`` and
    ``CTX_INCLUDE_PAUTH_REGS`` to 1. This enables pointer authentication in BL1,
    BL2, BL31, and the TSP if it is used.
 
+   These options are experimental features.
+
+   Note that Pointer Authentication is enabled for Non-secure world irrespective
+   of the value of these build flags if the CPU supports it.
+
    If ``ARM_ARCH_MAJOR == 8`` and ``ARM_ARCH_MINOR >= 3`` the code footprint of
    enabling PAuth is lower because the compiler will use the optimized
    PAuth instructions rather than the backwards-compatible ones.