irqchip/gic-v3: Add missing system register definitions

Define register definitions for ICH_VMCR_EL2, ICC_CTLR_EL1 and
ICH_VTR_EL2, ICC_BPR0_EL1, ICC_BPR1_EL1 registers.

Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@cavium.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>