arm: gic: Fix gic_set_cpu

gic_set_cpu can't be placed in init sections because
there are removed and this function can't be used by modules.

Should be the part of this patch:
"arm: zynq: gic: Use OF initialization"
(sha1: bfc0225ab4ce50abcd29b0dde5430c88f95d6f39)

Also coding style cleanup.

Signed-off-by: Michal Simek <monstr@monstr.eu>