Add a overload to CostTable which allows it to infer the size of the table.

Use it to avoid repeating ourselves too often. Also store MVT::SimpleValueType
in the TTI tables so they can be statically initialized, MVT's constructors
create bloated initialization code otherwise.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188095 91177308-0d34-0410-b5e6-96231b3b80d8