Remove backup ppc struct dis_private.

Remove backup ppc struct dis_private.

ppc-dis.c used a global struct whenever malloc failed to provide the
eight bytes of memory necessary for struct dis_private.  Which is
quite ridiculous.  If that malloc failed there is zero chance some
other malloc won't fail too.

	* ppc-dis.c (private): Delete variable.
	(get_powerpc_dialect): Don't segfault on NULL info->private_data.
	(powerpc_init_dialect): Don't use global private.