[TargetLowering] Change TargetLoweringBase::getPreferredVectorAction to take an MVT instead of an EVT. NFC

The main caller of this already has an MVT and several targets called getSimpleVT inside without checking isSimple. This makes the simpleness explicit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346180 91177308-0d34-0410-b5e6-96231b3b80d8
14 files changed