TFTF: Add ARMv8.5 BTI support in makefiles

This patch adds 'BRANCH_PROTECTION' build option in
TFTF makefiles which corresponds to that in TF-A.
The option values are documented in 'build-options.rst'

Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>
Change-Id: Iad5083aee339cec574acf5e7ab1fd8142877a122
10 files changed