PowerPC bc extended branch mnemonics and "y" hints

PowerPC bc extended branch mnemonics and "y" hints

This patch fixes a problem with disassembly of branch instructions
for processors complying with PowerPC ISA versions prior to version
2.0, ie. those that use "y" bit branch taken hints.  Many of the
extended bcctr and bclr mnemonics that should have disassembled with a
"-" suffix, ie. not taken, did not display the "-" due to the ordering
in powerpc_opcodes.  I believe it's been that way from the original
85dcf36d72b commit of ppc-opc.c.

I've also added a BH field (optional) to a few opcodes.  This gives
better disassembly in raw mode, showing the branch taken hint in the
mnemonic as is done for bc.  It would be reasonable to add a BH
field to all bcctr, bclr, and bctar extended mnemonics but that runs
into a small difficulty:  Currently we print all or none of the
optional operands.  That means for example that "bgectr cr2" would
display as "bgectr cr2,0" if a BH field is added to bgectr.

	* ppc-opc.c (XLBH_MASK): Subtract off BH field from BB_MASK.
	(powerpc_opcodes): Reorder bcctr and bclr extended mnemonics
	to favour printing of "-" branch hint when using the "y" bit.
	Allow BH field on bc{ctr,lr,tar}{,l}{-,+}.