KVM: arm64: nv: Fold GICv3 host trapping requirements into guest setup

KVM: arm64: nv: Fold GICv3 host trapping requirements into guest setup

Popular HW that is able to use NV also has a broken vgic implementation
that requires trapping.

On such HW, propagate the host trap bits into the guest's shadow
ICH_HCR_EL2 register, making sure we don't allow an L2 guest to bring
the system down.

This involves a bit of tweaking so that the emulation code correctly
poicks up the shadow state as needed, and to only partially sync
ICH_HCR_EL2 back with the guest state to capture EOIcount.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250225172930.1850838-15-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>