Improve code generation for vselect on SSE2:

Improve code generation for vselect on SSE2:
When checking the availability of instructions using the TLI, a 'promoted'
instruction IS available. It means that the value is bitcasted to another type
for which there is an operation. The correct check for the availablity of an
instruction is to check if it should be expanded.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142542 91177308-0d34-0410-b5e6-96231b3b80d8