MIPS: microMIPS: Add instruction utility macros.

Add two new macros for microMIPS. One checks if an exception was
taken in either microMIPS or classic MIPS mode. The other checks
if a microMIPS instruction is 16-bit or 32-bit in length.

[ralf@linux-mips.org: Removed unnecessary parenthesis as noted by
Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

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
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Patchwork: https://patchwork.linux-mips.org/patch/4924/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
(cherry picked from commit 49df26472338b935fd5781bf94a77a88b148a716)