MIPS: Use generic asm/unaligned.h

MIPS: Use generic asm/unaligned.h

The MIPS-specific asm/unaligned.h provides nothing that the generic
version doesn't - it simply uses MIPS-specific endianness macros in
place of generic ones & lacks support for
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS. Remove it & switch to using the
generic version to remove duplication.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14412/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>