PowerPC: Enable mfppr mfppr32, mtppr and mtppr32 extended mnemonics on POWER5

SPR 896 and the mfppr mfppr32, mtppr and mtppr32 extended mnemonics were added
in ISA 2.03, so enable them on POWER5 and later.

opcodes/
	* ppc-opc.c (powerpc_opcodes) <mfppr, mfppr32, mtppr, mtppr32>: Enable
	on POWER5 and later.

gas/
	* testsuite/gas/ppc/power5.s: New test.
	* testsuite/gas/ppc/power5.d: Likewise.
	* testsuite/gas/ppc/ppc.exp: Run it.
	* testsuite/gas/ppc/power7.s: Remove tests for mfppr, mfppr32, mtppr
	and mtppr32.
	* testsuite/gas/ppc/power7.d: Likewise.