Add support for regions and rework handling of the GICv3 redistributor.

Support more than one Re-Distributor region if that is described
by #redistributor-regions property in FDT.
Add two more structures: redist_region and redist_pcpu to improve
handling Re-Distributor.
Save re-distributor physical address for the purpose of ITS support.
Create separate FDT layer for GICv3

New FDT attachment will call generic functions from GICv3.
This will allow for easier FDT-based ITS attachment.
Minor white spaces clean-up in GICv3
Introduce bus capabilities to GICv3 - supports ITS as its subordinate.
Add more bus capabilities to GICv3

Still trying to keep as minimal as possible.
Introduce GICv3's ITS skeleton.

Allow for successful attach and resource acquisition.