target-ppc: Change core powerpc gdbstub bits to be XML-aware

Define GDB_CORE_XML and hack things similarly to ARM so that despite the
FP registers coming in between the GPRs and some status registers,
everything works out OK no matter which kind of GDB we're communicating
with.

It matters whether we're built to target 64-bit or 32-bit cores.  I
think there are still problems if we are debugging 32-bit programs on a
built-for-64-bit QEMU (QEMU will always send 64-bit registers), but I
don't know if there's a good way around that at the time being.

Signed-off-by: Nathan Froyd <froydnj@codesourcery.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6421 c046a42c-6fe2-441c-8c8c-71466251a162
