ARM: shmobile: marzen: Use DT for GIC

Current Marzen is using DT booting,
and r8a7779.dtsi already has GIC settings.

So, we can remove the C version of the GIC setup code,
instead rely on GIC information provided by DT.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>