Merge Branch Protection enablement

Branch Protection covers two ARMv8.3-A architecture features:
  - Branch Target Identification (BTI) to mitigate Return Oriented
    Programming (ROP) attacks.
  - Pointer Authentication (PAC) to mitigate Jump Oriented Programming
    (JOP) attacks.

This change enables BTI and PAC support. For details please refer to the
TS documentation.

Change-Id: I98f3e9fe584a3e5e7682b7dc19f22c8bf9e17b96
Signed-Off-By: Gyorgy Szing <gyorgy.szing@arm.com>