ARM: GICv3: introduce separate pending_irq structs for LPIs

ARM: GICv3: introduce separate pending_irq structs for LPIs

For the same reason that allocating a struct irq_desc for each
possible LPI is not an option, having a struct pending_irq for each LPI
is also not feasible. We only care about mapped LPIs, so we can get away
with having struct pending_irq's only for them.
Maintain a radix tree per domain where we drop the pointer to the
respective pending_irq. The index used is the virtual LPI number.
The memory for the actual structures has been allocated already per
device at device mapping time.
Teach the existing VGIC functions to find the right pointer when being
given a virtual LPI number.

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