arch-arm: Trap virtual accesses to GICv3 SGI registers

arch-arm: Trap virtual accesses to GICv3 SGI registers

According to GICv3 documentation, a virtual write (which means
HCR.IMO/FMO = 1) to ICC_SGI0R_EL1, ICC_SGI1R_EL1, ICC_ASGI1R_EL1 should
trap to EL2.

Change-Id: Ie7a952c2ff08590bb0c6e3854df567d714c2dc94
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/+/17990
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>