PowerPC instruction mask checks

PowerPC instruction mask checks

The instruction mask bits should never overlap any of the operands,
nor should operand bits overlap, but some operands weren't checked.
This patch arranges to check the omitted operands, using a mask
returned by the operand->insert function.  Some tweaking of various
insert functions is needed to support this: The error case must set
field bits.

Since I was looking at the insert functions, I tidied some dead code
and simplified some of the powerpc_operands entries.

gas/
	* config/tc-ppc.c (insn_validate): Don't ignore mask in
	PPC_OPSHIFT_INV case.  Call the insert function to calculate
	a mask.
opcodes/
	* ppc-opc.c (insert_arx, insert_ary, insert_rx, insert_ry, insert_ls),
	(insert_evuimm1_ex0, insert_evuimm2_ex0, insert_evuimm4_ex0),
	(insert_evuimm8_ex0, insert_evuimm_lt8, insert_evuimm_lt16),
	(insert_rD_rS_even, insert_off_lsp, insert_off_spe2, insert_Ddd):
	Don't return zero on error, insert mask bits instead.
	(insert_sd4h, extract_sd4h, insert_sd4w, extract_sd4w): Delete.
	(insert_sh6, extract_sh6): Delete dead code.
	(insert_sprbat, insert_sprg): Use unsigned comparisions.
	(powerpc_operands <OIMM>): Set shift count rather than using
	PPC_OPSHIFT_INV.
	<SE_SDH, SE_SDW>: Likewise.  Don't use insert/extract functions.