armv8/gic: Fix GIC v2 initialization

armv8/gic: Fix GIC v2 initialization

Initialize all GICD_IGROUPRn registers and set up GICC_CTLR to enable
interrupts to the primary CPU. This fixes issues seen after booting a
Linux kernel from U-Boot.

Suggested-by: Marc Zyngier <marc.zyngier@arm.com>
Suggested-by: Mark Rutland <mark.rutland@arm.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>