dev-arm: Set ICV_PMR_EL1-ICH_VMCR_EL2 mapping on reads

dev-arm: Set ICV_PMR_EL1-ICH_VMCR_EL2 mapping on reads

Reading ICV_PMR_EL1 should return the value the VMCR_EL2.VPMR bits
which are aliased to the register.

Change-Id: Id3e6dfb196f3726edaa3eddb244765598ed62334
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Jan-Peter Larsson <jan-peter.larsson@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/16545
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>