[RegisterBankInfo] Adapt the copy cost logic to give something sane by default.
[RegisterBankInfo] Adapt the copy cost logic to give something sane by default.

The generic implementation stated that all copies were free, which is
unlikely. Now, only the copies within the same register bank are free.
We assume they will get coalesced.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@272085 91177308-0d34-0410-b5e6-96231b3b80d8

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