Enable MTE support

Enable MTE support by adding memory tag option in Makefile
This option is available only when ARMv8.5-MemTag is implemented

MTE options are added in latest clang and armclang compiler which
support below options:
for clang <version 11.0.0>
1. -march=arm8.5-a+memtag
2. -fsanitize=memtag

for armclang <version 6.12>
1. -march=arm8.5-a+memtag
2. -mmemtag-stack

Set the option SUPPORT_STACK_MEMTAG=yes to enable memory stack tagging.

Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: I4e0bbde4e9769ce03ead6f550158e22f32c1c413
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index 69e103d..e1c6c8f 100644
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -667,6 +667,11 @@
    cluster platforms). If this option is enabled, then warm boot path
    enables D-caches immediately after enabling MMU. This option defaults to 0.
 
+-  ``SUPPORT_STACK_MEMTAG``: This flag determines whether to enable memory
+   tagging for stack or not. It accepts 2 values: ``yes`` and ``no``. The
+   default value of this flag is ``no``. Note this option must be enabled only
+   for ARM architecture greater than Armv8.5-A.
+
 GICv3 driver options
 --------------------