arch: arm: enable PACBTI support

As part of enabling PACBTI support:
- Add config options to enforce PAC and BTI features
- Enable these config options based on the branch protection choice
  selected for `ARM_PACBTI`
- Enforce PACBTI, based on the new config options, by enabling
  corresponding PACBTI bits in CONTROL register and in FVP.

Signed-off-by: Sudan Landge <sudan.landge@arm.com>