Only allow 32-bit/64-bit registers for bndcl/bndcu/bndcn

gas/testsuite/

	* gas/i386/mpx.s: Remove bndcl/bndcu/bndcn tests with AX.
	* gas/i386/x86-64-mpx.s: Likwise.

	* gas/i386/mpx.d: Updated.
	* gas/i386/x86-64-mpx.d: Likewise.

opcodes/

	* i386-dis.c (intel_operand_size): Move v_bnd_mode alongside the
	default case.
	(OP_E_register): Move v_bnd_mode alongside m_mode.
	* i386-opc.tbl (bndcl, bndcu, bndcn): Split 32- and 64-bit variants.
	Drop Reg16 and Disp16. Add NoRex64.
	(bndmk, bndmov, bndldx, bndstx): Drop Disp16.
	* i386-tbl.h: Re-generate.
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