ARM: VGIC: rework gicv[23]_update_lr to not use pending_irq

ARM: VGIC: rework gicv[23]_update_lr to not use pending_irq

The functions to actually populate a list register were accessing
the VGIC internal pending_irq struct, although they should be abstracting
from that.
Break the needed information down to remove the reference to pending_irq
from gic-v[23].c.

Signed-off-by: Andre Przywara <andre.przywara@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>