sse.md (avx2_vec_dupv4df): Use v instead of x constraint, use maybe_evex prefix inste...

sse.md (avx2_vec_dupv4df): Use v instead of x constraint, use maybe_evex prefix instead of vex.

	* config/i386/sse.md (avx2_vec_dupv4df): Use v instead of x
	constraint, use maybe_evex prefix instead of vex.
	(vec_dupv4sf): Use v constraint instead of x for output
	operand except for noavx alternative, use Yv constraint
	instead of x for input.  Use maybe_evex prefix instead of vex.
	(*vec_dupv4si): Likewise.
	(*vec_dupv2di): Likewise.

	* gcc.target/i386/avx512vl-vbroadcast-1.c: New test.

From-SVN: r236566