sse.md (*vec_concatv2di): Add x86_avx512dq v=Yv,rm alternative.

sse.md (*vec_concatv2di): Add x86_avx512dq v=Yv,rm alternative.

	* config/i386/sse.md (*vec_concatv2di): Add x86_avx512dq v=Yv,rm
	alternative.  Change x=xm,C alternative to v=vm,C, x=x,x alternative
	to v=Yv,Yv and x=x,m to v=v,m.  Use maybe_evex prefix attribute
	instead of vex for the last two above mentioned alternatives.

	* gcc.target/i386/avx512dq-concatv2di-1.c: New test.
	* gcc.target/i386/avx512vl-concatv2di-1.c: New test.
	* gcc.target/i386/sse2-init-v2di-2.c: Adjust expected vec_concatv2di
	alternative number.

From-SVN: r237028