MIPS: Include asm/setup.h for cpu_cache_init()

MIPS: Include asm/setup.h for cpu_cache_init()

arch/mips/mm/cache.c provides our implementation of the cpu_cache_init()
function, but doesn't include the asm/setup.h header which declares it.
This leads to a warning from sparse:

  arch/mips/mm/cache.c:274:6: warning: symbol 'cpu_cache_init' was not
    declared. Should it be static?

Fix this by including asm/setup.h to get the declaration of
cpu_cache_init().

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: trivial@kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/17168/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>