arm64: gic: Add power up sequence for GIC-600

Arm's GIC-600 features a Power Register (GICR_PWRR),
which needs to be programmed to enable redistributor
operation. Power on the redistributor and  wait until
the power on state is reflected by checking the bit
GICR_PWRR.RDPD == 0. While running U-Boot in EL3
without enabling this register, GICR_WAKER.ChildrenAsleep
bit is not getting cleared and loops infinitely.
This register(GICR_PWRR) must be programmed to mark the frame
as powered on, before accessing other registers in the frame.
Rest of initialization sequence remains the same.

ARM GIC-600 IP complies with ARM GICv3 architecture.
Enable this config if GIC-600 IP present.

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>