Correct powerpc spe opcode lookup

Correct powerpc spe opcode lookup

Defining SPE2_OPCD_SEGS as 13 discounts the possibility that we'd
ever look up spe2_opcd_indices[14..16], which I think is possible.
Extend that array to size 16+1, using the macros we use to index the
array.  Similarly use the index macros for PPC_OPCD_SEGS and
VLE_OPCD_SEGS.

	* ppc-dis.c (PPC_OPCD_SEGS): Define using PPC_OP.
	(VLE_OPCD_SEGS, SPE2_OPCD_SEGS): Similarly, using macros used to
	partition opcode space for index lookup.