MIPS: Make the CODE10 operand code consistent between ISAs

MIPS: Make the CODE10 operand code consistent between ISAs

This change moves the microMIPS 10-bit uninterpreted immediate code
embedded at bits 25..16 in the SYSCALL, WAIT, SDBBP and HYPCALL
instructions from `B' over to `+J' which is the operand code used in
the standard MIPS instruction set for a similar code embedded at bits
20..11, currently used by HYPCALL only in that set.

	opcodes/
	* micromips-opc.c (decode_micromips_operand): Rename `B' to `+J'.
	(micromips_opcodes): Use "+J" in place of "B" for "hypcall",
	"sdbbp", "syscall" and "wait".

	include/opcode/
	* mips.h: Document the move of `MICROMIPSOP_*_CODE10' from `B'
	over to `+J'.