xen/arm: Add FnV field in hsr_*abt

xen/arm: Add FnV field in hsr_*abt

FnV (FAR not Valid) bit was introduced by ARMv8 in both AArch32 and
AArch64 (See D7-2275, D7-2277, G6-4958, G6-4962 in ARM DDI 0487B.a).

Note the new revision of ARMv8 defined more bits in HSR. They haven't
been added at the moment because we have no use of them in Xen.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>