TF-A: Add ARMv8.5 'bti' build option

This patch adds BRANCH_PROTECTION = 4 'bti' build option
which turns on branch target identification mechanism.

Change-Id: I32464a6b51726a100519f449a95aea5331f0e82d
Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>
2 files changed