Check invalid mask registers

Check invalid mask registers

In 32-bit, the REX_B bit in the 3-byte VEX prefix is ignored and the
the highest bit in VEX.vvvv is either 1 or ignored.  In 64-bit, we
need to check invalid mask registers.

gas/

	PR binutis/20705
	* testsuite/gas/i386/i386.exp: Run x86-64-opcode-bad.
	* testsuite/gas/i386/x86-64-opcode-bad.d: New file.
	* testsuite/gas/i386/x86-64-opcode-bad.s: Likewise.

opcodes/

	PR binutis/20705
	* i386-dis.c (get_valid_dis386): Ignore the REX_B bit and
	the highest bit in VEX.vvvv for the 3-byte VEX prefix in
	32-bit mode.  Don't check vex.register_specifier in 32-bit
	mode.
	(OP_E_register): Check invalid mask registers.
	(OP_G): Likewise.
	(OP_VEX): Likewise.