arch-arm: Check if PAC is implemented before executing insts

arch-arm: Check if PAC is implemented before executing insts

If Armv8.3-PAuth (PAC) extension is not supported, most instrucions
will trigger an Undefined Instruction fault; except for a group of
them living in the HINT space; those should be treated as NOP.

Change-Id: Idec920ed15e0310ec9132a3cb3701cdb7e7cf9d1
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/33455
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>