arch-arm: R/W interface to AArch32 HCR2 misc reg

arch-arm: R/W interface to AArch32 HCR2 misc reg

This patch implements read/write interfaces to HCR2 AArch32 register,
which is mapped to the upper 32 bits of HCR_EL2.

Change-Id: I996023f3ad8233457d19de8a506ebcf106409165
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/22832
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>