KVM: arm64: Handle physical FIQ as an IRQ while running a guest

As we we now entertain the possibility of FIQ being used on the host,
treat the signalling of a FIQ while running a guest as an IRQ,
causing an exit instead of a HYP panic.

Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>