ARM: GICv3: setup number of LPI bits for a GICv3 guest

ARM: GICv3: setup number of LPI bits for a GICv3 guest

The host supports a certain number of LPI identifiers, as stored in
the GICD_TYPER register.
Store this number from the hardware register in vgic_v3_hw to allow
injecting the very same number into a guest (Dom0).
DomUs get the legacy number of 10 bits here, since for now it only sees
SPIs, so it does not need more. This should be revisited once we get
proper DomU ITS support.

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