i386: Add v<any_shift:insn>v4qi3 expander

i386: Add v<any_shift:insn>v4qi3 expander

Also, move v<any_shift:insn>v8qi3 expander to a better place and enable
it with TARGET_MMX_WITH_SSE.  Remove handling of V8QImode from
ix86_expand_vecop_qihi2 since all partial QI->HI vector modes expand
via ix86_expand_vecop_qihi_partial.

gcc/ChangeLog:

	* config/i386/i386-expand.cc (ix86_expand_vecop_qihi2):
	Remove handling of V8QImode.
	* config/i386/mmx.md (v<insn>v8qi3): Move from sse.md.
	Call ix86_expand_vecop_qihi_partial.  Enable for TARGET_MMX_WITH_SSE.
	(v<insn>v4qi3): Ditto.
	* config/i386/sse.md (v<insn>v8qi3): Remove.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/vect-shiftv4qi.c (dg-options):
	Remove -ftree-vectorize.
	* gcc.target/i386/vect-shiftv8qi.c (dg-options): Ditto.
	* gcc.target/i386/vect-vshiftv4qi.c: New test.
	* gcc.target/i386/vect-vshiftv8qi.c: New test.