This patch add gicv3 support to uboot armv8 platform.

Changes for v2:
  - rename arm/cpu/armv8/gic.S with arm/lib/gic_64.S
  - move smp_kick_all_cpus() from gic.S to start.S, it would be
    implementation dependent.
  - Each core initialize it's own ReDistributor instead of master
    initializeing all ReDistributors. This is advised by arnab.basu
    <arnab.basu@freescale.com>.

Signed-off-by: David Feng <fenghua@phytium.com.cn>