rs6000: Improve vsx_init_v4si

rs6000: Improve vsx_init_v4si

This changes vsx_init_v4si to be an expander.  That way, no special
cases are needed anymore for special arguments: the normal RTL passes
can deal with it.

	* config/rs6000/rs6000-p8swap.c (rtx_is_swappable_p): Adjust.
	* config/rs6000/rs6000-protos.h (rs6000_split_v4si_init): Delete.
	* config/rs6000/rs6000.c (rs6000_expand_vector_init): Always force
	the elements into a register.
	(rs6000_split_v4si_init_di_reg): Delete.
	(rs6000_split_v4si_init): Delete.
	* config/rs6000/vsx.md (unspec): Delete UNSPEC_VSX_VEC_INIT.
	(vsx_init_v4si): Rewrite as a define_expand.

From-SVN: r262930