[CostModel][X86] Merge getTypeBasedIntrinsicInstrCost into getIntrinsicInstrCost

For the few non type based intrinsic cases we can just check for !isTypeBasedOnly() to access the args directly.

I don't think we have a need to keep getTypeBasedIntrinsicInstrCost in BasicTTIImpl.h any more and can do a similar merge there as well - but it's a messier refactor and will take a while.