Update 'struct gic_redists' to consolidate all per-cpu redistributor information into a new 'struct redist_pcpu'. Additionaly, remove the current interface in GICv3 driver (GICV3_IVAR_REDIST_VADDR) which provides the redistributor virtual address, and provide a new interface (GICV3_IVAR_REDIST) which retrieves the above per-cpu data.
This per-cpu redistributor struct will be later used to improve GIC ITS setup.
While there, remove some unused fields in gic_v3_var.h interface. No functional changes.