KVM: arm64: nv: Honor HFGITR_EL2.ERET being set

If the L1 hypervisor decides to trap ERETs while running L2,
make sure we don't try to emulate it, just like we wouldn't
if it had its NV bit set.

The exception will be reinjected from the core handler.

Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240419102935.1935571-9-maz@kernel.org


Signed-off-by: Marc Zyngier <maz@kernel.org>