Disallow 3-operand cmp[l][i] for ppc64

Disallow 3-operand cmp[l][i] for ppc64

cmp[l][o] get an optional L field only when generating 32-bit code.
dcbf, tlbie and tlbiel keep their optional L field, ditto for R field
of tbegin.  cmprb, tsr., wlcr[all] and mtsle all change to a
compulsory L field.

L field of dcbf and wclr is 2 bits.

	PR 20641
include/
	* opcode/ppc.h (PPC_OPERAND_OPTIONAL32): Define.
opcodes/
	* ppc-opc.c (L): Make compulsory.
	(LOPT): New, optional form of L.
	(HTM_R): Define as LOPT.
	(L0, L1): Delete.
	(L32OPT): New, optional for 32-bit L.
	(L2OPT): New, 2-bit L for dcbf.
	(SVC_LEC): Update.
	(L2): Define.
	(insert_l0, extract_l0, insert_l1, extract_l2): Delete.
	(powerpc_opcodes <cmpli, cmpi, cmpl, cmp>): Use L32OPT.
	<dcbf>: Use L2OPT.
	<tlbiel, tlbie>: Use LOPT.
	<wclr, wclrall>: Use L2.
gas/
	* config/tc-ppc.c (md_assemble): Handle PPC_OPERAND_OPTIONAL32.
	* testsuite/gas/ppc/power8.s: Provide tbegin. operand.
	* testsuite/gas/ppc/power9.d: Update cmprb disassembly.