ARM: GIC: remove assembly ifdefs from gic.h

With multi irq handler and all GIC users converted to it, we don't need
asm/hardware/gic.h to be included in assembly. Clean-up ifdefs and
unnecessary includes.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Olof Johansson <olof@lixom.net>