ti: k3: common: Enable GICv3 support

Do proper initialization of GIC V3. This will allow CP15 access to GIC
from "normal world" (aka HLOS) via mrc/mcr calls.

K3 SoC family uses GICv3 compliant GIC500 without compatibility for
legacy GICv2.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Benjamin Fair <b-fair@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>