ARM: GICv3 ITS: allocate device and collection table

ARM: GICv3 ITS: allocate device and collection table

Each ITS maps a pair of a DeviceID (for instance derived from a PCI
b/d/f triplet) and an EventID (the MSI payload or interrupt ID) to a
pair of LPI number and collection ID, which points to the target CPU.
This mapping is stored in the device and collection tables, which software
has to provide for the ITS to use.
Allocate the required memory and hand it over to the ITS.

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