XCOFF disassembler

XCOFF disassembler

xcoff (32-bit) objdump accepted but ignored -M options unless
-mpowerpc was also given.  This patch fixes that, leaving the default
as -Mpwr for xcoff.  I've also enabled more tests for xcoff targets.

binutils/
	* configure.ac: Add objdump_private_desc_xcoff for rs6000.
	* configure: Regenerate.
gas/
	* testsuite/gas/ppc/aix.exp: Run for rs6000 too.
	* testsuite/gas/ppc/ppc.exp: Run more tests for non-ELF targets.
	* testsuite/gas/ppc/machine.d: Don't run for PE targets.
opcodes/
	* disassemble.c (disassembler): Use bfd_arch_powerpc entry for
	bfd_arch_rs6000.
	* disassemble.h (print_insn_rs6000): Delete.
	* ppc-dis.c (powerpc_init_dialect): Handle rs6000.
	(disassemble_init_powerpc): Call powerpc_init_dialect for rs6000.
	(print_insn_rs6000): Delete.