MIPS: Optimize uasm insn lookup.

MIPS: Optimize uasm insn lookup.

Instead of doing a linear search through the insn_table for each
instruction, use the opcode as direct index into the table.  This will
give constant time lookup performance as the number of supported
opcodes increases.  Make the tables const as they are only ever read.
For uasm-mips.c sort the table alphabetically, and remove duplicate
entries, uasm-micromips.c was already sorted and duplicate free.
There is a small savings in object size as struct insn loses a field:

$ size arch/mips/mm/uasm-mips.o arch/mips/mm/uasm-mips.o.save
   text	   data	    bss	    dec	    hex	filename
  10040	      0	      0	  10040	   2738	arch/mips/mm/uasm-mips.o
   9240	   1120	      0	  10360	   2878	arch/mips/mm/uasm-mips.o.save

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16365/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>