PowerPC fix for the gdb.arch/powerpc-power10.exp test.

PowerPC fix for the gdb.arch/powerpc-power10.exp test.

The mnemonics for the pmxvf16ger*, pmxvf32ger*,pmxvf64ger*, pmxvi4ger8*,
pmxvi8ger4*, pmxvi16ger2* instructions were officially changed to
pmdmxvf16ger*, pmdmxvf32ger*, pmdmxvf64ger*, pmdmxvi4ger8*, pmdmxvi8ger4*,
pmdmxvi16ger* respectively.  The old mnemonics are still supported by the
assembler as extended mnemonics.  The disassembler generates the new
mnemonics.  The name changes occurred in commit:

  commit bb98553cad4e017f1851153fa5de91f2cee98fb2
  Author: Peter Bergner <bergner@linux.ibm.com>
  Date:   Sat Oct 8 16:19:51 2022 -0500

    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.

The above commit results in about 224 failures on Power 10 since the
disassembled names do not match the expected names in the test.  This
patch updates the expected names in the test to match the values produced
by the disassembler.

This patch updates file gdb.arch/powerpc-power10.exp with the new expected
values to the instructions.  The comment giving the name of the instruction
for each binary value in the file gdb.arch/powerpc-power10.c is updated
with the new name.   There are no functional changes in file
gdb.arch/powerpc-power10.c.