Add extended mnemonics for bctar. Fix setting of 'at' branch hints.

opcodes/
	PR gas/24349
	* ppc-opc.c (valid_bo_pre_v2): Add comments.
	(valid_bo_post_v2): Add support for 'at' branch hints.
	(insert_bo): Only error on branch on ctr.
	(get_bo_hint_mask): New function.
	(insert_boe): Add new 'branch_taken' formal argument.  Add support
	for inserting 'at' branch hints.
	(extract_boe): Add new 'branch_taken' formal argument.  Add support
	for extracting 'at' branch hints.
	(insert_bom, extract_bom, insert_bop, extract_bop): New functions.
	(BOE): Delete operand.
	(BOM, BOP): New operands.
	(RM): Update value.
	(XLYLK, XLYLK_MASK, XLYBB_MASK): Delete.
	(powerpc_opcodes) <bc-, bcl-, bca-, bcla-, bclr-, bclrl-, bcctr-,
	bcctrl-, bctar-, bctarl->: Replace BOE with BOM.
	(powerpc_opcodes) <bc+, bcl+, bca+, bcla+, bclr+, bclrl+, bcctr+,
	bcctrl+, bctar+, bctarl+>: Replace BOE with BOP.
	<bdnztar, bdnztarl, bdztar, bdztarl, btar, btarl, bdnztar-, bdnztarl-,
	bdnztar+, bdnztarl+, bdztar-, bdztarl-, bdztar+, bdztarl+, bgetar,
	bnltar, bgetarl, bnltarl, bletar, bngtar, bletarl, bngtarl, bnetar,
	bnetarl, bnstar, bnutar, bnstarl, bnutarl, bgetar-, bnltar-, bgetarl-,
	bnltarl-, bletar-, bngtar-, bletarl-, bngtarl-, bnetar-, bnetarl-,
	bnstar-, bnutar-, bnstarl-, bnutarl-, bgetar+, bnltar+, bgetarl+,
	bnltarl+, bletar+, bngtar+, bletarl+, bngtarl+, bnetar+, bnetarl+,
	bnstar+, bnutar+, bnstarl+, bnutarl+, blttar, blttarl, bgttar, bgttarl,
	beqtar, beqtarl, bsotar, buntar, bsotarl, buntarl, blttar-, blttarl-,
	bgttar-, bgttarl-, beqtar-, beqtarl-, bsotar-, buntar-, bsotarl-,
	buntarl-, blttar+, blttarl+, bgttar+, bgttarl+, beqtar+, beqtarl+,
	bsotar+, buntar+, bsotarl+, buntarl+, bdnzftar, bdnzftarl, bdzftar,
	bdzftarl, bftar, bftarl, bftar-, bftarl-, bftar+, bftarl+, bdnzttar,
	bdnzttarl, bdzttar, bdzttarl, bttar, bttarl, bttar-, bttarl-, bttar+,
	bttarl+>: New extended mnemonics.

gas/
	PR gas/24349
	* testsuite/gas/ppc/power8.s: (bdnztar, bdnztarl, bdztar, bdztarl,
	btar, btarl, bdnztar-, bdnztarl-, bdnztar+, bdnztarl+, bdztar-,
	bdztarl-, bdztar+, bdztarl+, bgetar, bnltar, bgetarl, bnltarl,
	bletar, bngtar, bletarl, bngtarl, bnetar, bnetarl, bnstar, bnutar,
	bnstarl, bnutarl, bgetar-, bnltar-, bgetarl-, bnltarl-, bletar-,
	bngtar-, bletarl-, bngtarl-, bnetar-, bnetarl-, bnstar-, bnutar-,
	bnstarl-, bnutarl-, bgetar+, bnltar+, bgetarl+, bnltarl+, bletar+,
	bngtar+, bletarl+, bngtarl+, bnetar+, bnetarl+, bnstar+, bnutar+,
	bnstarl+, bnutarl+, blttar, blttarl, bgttar, bgttarl, beqtar,
	beqtarl, bsotar, buntar, bsotarl, buntarl, blttar-, blttarl-,
	bgttar-, bgttarl-, beqtar-, beqtarl-, bsotar-, buntar-, bsotarl-,
	buntarl-, blttar+, blttarl+, bgttar+, bgttarl+, beqtar+, beqtarl+,
	bsotar+, buntar+, bsotarl+, buntarl+, bdnzftar, bdnzftarl, bdzftar,
	bdzftarl, bftar, bftarl, bftar-, bftarl-, bftar+, bftarl+, bdnzttar,
	bdnzttarl, bdzttar, bdzttarl, bttar, bttarl, bttar-, bttarl-, bttar+,
	bttarl+): Add tests of extended mnemonics.
	* testsuite/gas/ppc/power8.d: Likewise.  Update previous bctar tests
	to expect new extended mnemonics.
	* testsuite/gas/ppc/a2.s: <bc, bc-, bc+, bcl, bcl-, bcl+>: Update test
	to not use illegal BO value.  Use a more convenient BI value.
	* testsuite/gas/ppc/a2.d: Update tests for new expect output.