dev-arm: Add read/writeBanked helpers to GICv3

These will be used by AA64 security banked registers in GICv3.

Change-Id: Ia980c4f5c14187ab9c18da1d1d596562644111ae
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20624
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
2 files changed