[POWERPC] Import updated version of ppc disassembly code for xmon

This includes:
 * version 1.24 of ppc-dis.c
 * version 1.88 of ppc-opc.c
 * version 1.23 of ppc.h

I can't vouch for the accuracy etc. of these changes, but it brings
us into line with binutils - and from a cursory test appears to work
fine.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>