ARM: GIC: Allow tweaking the active and pending state of an IRQ

ARM: GIC: Allow tweaking the active and pending state of an IRQ

When playing around with hardware mapped, level triggered virtual IRQs,
there is the need to explicitly set the active or pending state of an
interrupt at some point.
To prepare the GIC for that, we introduce a set_active_state() and a
set_pending_state() function to let the VGIC manipulate the state of
an associated hardware IRQ.
This takes care of properly setting the _IRQ_INPROGRESS bit.

Signed-off-by: Andre Przywara <andre.przywara@linaro.org>
Reviewed-by: Julien Grall <julien.grall@arm.com>