PowerPC: Add support for RFC02658 - MMA+ Outer-Product Instructions

gas/
	* config/tc-ppc.c (md_assemble): Only check for prefix opcodes.
	* testsuite/gas/ppc/rfc02658.s: New test.
	* testsuite/gas/ppc/rfc02658.d: Likewise.
	* testsuite/gas/ppc/ppc.exp: Run it.

opcodes/
	* ppc-opc.c (XMSK8, P_GERX4_MASK, P_GERX2_MASK, XX3GERX_MASK): New.
	(powerpc_opcodes): Add dmxvi8gerx4pp, dmxvi8gerx4, dmxvf16gerx2pp,
	dmxvf16gerx2, dmxvbf16gerx2pp, dmxvf16gerx2np, dmxvbf16gerx2,
	dmxvi8gerx4spp, dmxvbf16gerx2np, dmxvf16gerx2pn, dmxvbf16gerx2pn,
	dmxvf16gerx2nn, dmxvbf16gerx2nn, pmdmxvi8gerx4pp, pmdmxvi8gerx4,
	pmdmxvf16gerx2pp, pmdmxvf16gerx2, pmdmxvbf16gerx2pp, pmdmxvf16gerx2np,
	pmdmxvbf16gerx2, pmdmxvi8gerx4spp, pmdmxvbf16gerx2np, pmdmxvf16gerx2pn,
	pmdmxvbf16gerx2pn, pmdmxvf16gerx2nn, pmdmxvbf16gerx2nn.