Range of element index is too large on MIPS MSA element selection instructions.

Range of element index is too large on MIPS MSA element selection instructions.

The element index range for the following MIPS MSA instructions: sldi, splati,
copy_s, copy_u, insert and insve is 1 bit too large.  This patch fixes this issue.

ChangeLog:

	gas/testsuite/gas/mips/
	* msa.s: Reduced maximum element index range for sldi, splati,
	copy_s, copy_u, insert and insve instructions.
	* msa64.s: Likewise.
	* micromips@msa.d: Likewise.
	* micromips@msa64.d: Likewise.
	* msa.d: Likewise.
	* msa64.d: Likewise.

	include/opcode/
	* mips.h: Updated description of +o, +u, +v and +w for MIPS and
	microMIPS.

	opcodes/
	* micromips-opc.c (decode_micromips_operand): Reduced range of +o, +u,
	+v and +w.
	(micromips_opcodes): Reduced element index range for sldi, splati,
	copy_s, copy_u, insert and insve instructions.
	* opcodes/mips-opc.c (decode_mips_operand): Reduced range of +o, +u,
	+v and +w.
	(mips_builtin_opcodes): Reduced element index range for sldi, splati,
	copy_s, copy_u, insert and insve instructions.