dev-arm: Set ICV_IGRPEN<n>_EL1-ICH_VMCR_EL2 mapping on reads

dev-arm: Set ICV_IGRPEN<n>_EL1-ICH_VMCR_EL2 mapping on reads

Reading ICV_IGRPEN<n>_EL1 should return the value of VMCR_EL2.VENG0 and
VMCR_EL2.VENG1 bits.

Change-Id: Ia5d748cf60ba074cccf4c127ac479c5cb881773d
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/16544
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>