arm: driver for CoreLink GIC-400 Generic Interrupt Controller

arm: driver for CoreLink GIC-400 Generic Interrupt Controller

- GICC, GICD and GICH initialization;

- interrupts routing, acking and EOI;

- interrupt injection into guests;

- maintenance interrupt handler, that takes care of EOI physical
  interrupts on behalf of the guest;

- a function to remap the virtual cpu interface into the guest address
  space, where the guest expect the GICC to be.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>