arm: dev: Replace ArmISA::MiscReg with RegVal in the GIC v3 model.

Other dev code was already switched over. This code was written before
the switch over (or unaware of it), and checked in after.

Change-Id: Ibb9e9e4300d01cc46e4dae668274debc2a4989ba
Reviewed-on: https://gem5-review.googlesource.com/c/15755
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2 files changed