irqchip/gic-v3: Expose GICD_TYPER in the rdist structure

Instead of exposing the GIC distributor IntID field in the rdist
structure that is passed to the ITS, let's replace it with a
copy of the whole GICD_TYPER register. We are going to need
some of this information at a later time.

No functionnal change.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>