PR27676, PowerPC missing extended dcbt, dcbtst mnemonics

PR27676, PowerPC missing extended dcbt, dcbtst mnemonics

Note that this doesn't implement the ISA to the letter regarding
dcbtds (and dcbtstds), which says that the TH field may be zero.  That
doesn't make sense because allowing TH=0 would mean you no long have a
dcbtds but rather a dcbtct instruction.  I'm interpreting the ISA
wording about allowing TH=0 to mean that the TH field of dcbtds is
optional (in which case the TH value is 0b1000).

opcodes/
	PR 27676
	* ppc-opc.c (DCBT_EO): Move earlier.
	(insert_thct, extract_thct, insert_thds, extract_thds): New functions.
	(powerpc_operands): Add THCT and THDS entries.
	(powerpc_opcodes): Add dcbtstct, dcbtstds, dcbna, dcbtct, dcbtds.
gas/
	* testsuite/gas/ppc/pr27676.d,
	* testsuite/gas/ppc/pr27676.s: New test.
	* testsuite/gas/ppc/ppc.exp: Run it.
	* testsuite/gas/ppc/dcbt.d: Update.
	* testsuite/gas/ppc/power4_32.d: Update.