Account for vector splat GPR->XMM move cost

Account for vector splat GPR->XMM move cost

The following also accounts for a GPR->XMM move cost for splat
operations and properly guards eliding the cost when moving from
memory only for SSE4.1 or HImode or larger operands.  This
doesn't fix the PR fully yet.

	PR target/109944
	* config/i386/i386.cc (ix86_vector_costs::add_stmt_cost):
	For vector construction or splats apply GPR->XMM move
	costing.  QImode memory can be handled directly only
	with SSE4.1 pinsrb.