ARM: dts: Declare the gic as a15 compatible for exynos5250

The GIC in the exynos5250 SoC is A15 compliant. Show this through
the device tree, so that we can use the GIC for KVM.

Also add the respective A15 memory regions and interrupt links.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>