MIPS: microMIPS: uasm: Add microMIPS micro assembler support.

MIPS: microMIPS: uasm: Add microMIPS micro assembler support.

Add new file 'uasm-micromips.c' that allows the micro assembler
to generate microMIPS ISA code. It can be included in the kernel
alongside the classic ISA as long as the platform supports the
microMIPS ISA.

Signed-off-by: Steven J. Hill <sjhill@mips.com>
Cc: linux-mips@linux-mips.org
Cc: cernekee@gmail.com
Cc: kevink@paralogos.com
Cc: ddaney.cavm@gmail.com
Patchwork: https://patchwork.linux-mips.org/patch/4923/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>