i386: Clear upper bits of XMM register for V4HFmode/V2HFmode operations [PR110762]

Similar like r14-2786-gade30fad6669e5, the patch is for V4HF/V2HFmode.

gcc/ChangeLog:

	PR target/110762
	* config/i386/mmx.md (<insn><mode>3): Changed from define_insn
	to define_expand and break into ..
	(<insn>v4hf3): .. this.
	(divv4hf3): .. this.
	(<insn>v2hf3): .. this.
	(divv2hf3): .. this.
	(movd_v2hf_to_sse): New define_expand.
	(movq_<mode>_to_sse): Extend to V4HFmode.
	(mmxdoublevecmode): Ditto.
	(V2FI_V4HF): New mode iterator.
	* config/i386/sse.md (*vec_concatv4sf): Extend to hanlde V8HF
	by using mode iterator V4SF_V8HF, renamed to ..
	(*vec_concat<mode>): .. this.
	(*vec_concatv4sf_0): Extend to handle V8HF by using mode
	iterator V4SF_V8HF, renamed to ..
	(*vec_concat<mode>_0): .. this.
	(*vec_concatv8hf_movss): New define_insn.
	(V4SF_V8HF): New mode iterator.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr110762-v4hf.c: New test.