sse.md (*vec_extractv4sf_0, [...]): Use v instead of x in vex or maybe_vex alternativ...

sse.md (*vec_extractv4sf_0, [...]): Use v instead of x in vex or maybe_vex alternatives...

	* config/i386/sse.md (*vec_extractv4sf_0, *sse4_1_extractps,
	*vec_extractv4sf_mem, vec_extract_lo_v16hi, vec_extract_hi_v16hi,
	vec_extract_lo_v32qi, vec_extract_hi_v32qi): Use v instead of x
	in vex or maybe_vex alternatives, use maybe_evex instead of vex
	in prefix.

From-SVN: r235970