socfpga: fix include guard in misc.h (arch vs. global)

The file arch/arm/mach-socfpga/include/mach/misc.h used the same include
guard as the global include/misc.h.

Fix this by giving the arch file an arch prefix.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Reviewed-by: Ley Foon Tan <ley.foon.tan@intel.com>