[RegisterBankInfo] Add a size argument for the cost of copy.

[RegisterBankInfo] Add a size argument for the cost of copy.

The cost of a copy may be different based on how many bits we have to
copy around. E.g., a 8-bit copy may be different than a 32-bit copy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272084 91177308-0d34-0410-b5e6-96231b3b80d8