PowerPC register numbers in DWARF

This makes gas .cfi output to .debug_frame match register numbering
emitted by gcc.  md_reg_eh_frame_to_debug_frame follows the ABI,
targets not using it, notably Linux, don't.

	* config/tc-ppc.h (md_reg_eh_frame_to_debug_frame): Match current
	gcc behaviour.
	* config/te-aix.h: New file.
	* configure.tgt: Use em=aix for powerpc-aix.