MIPS: Include elf-randomize.h for arch_mmap_rnd() & arch_randomize_brk()

MIPS: Include elf-randomize.h for arch_mmap_rnd() & arch_randomize_brk()

arch/mips/mm/mmap.c provides our implementations of the arch_mmap_rnd()
& arch_randomize_brk() functions, but doesn't include the
linux/elf-randomize.h header which declares them. This leads to warnings
from sparse:

  arch/mips/mm/mmap.c:146:15: warning: symbol 'arch_mmap_rnd' was not
    declared. Should it be static?
  arch/mips/mm/mmap.c:190:15: warning: symbol 'arch_randomize_brk' was
    not declared. Should it be static?

Fix this by including linux/elf-randomize.h to get the declarations of
arch_mmap_rnd() & arch_randomize_brk().

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/17171/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>