Fixed AVR hack to use updated normalizeSpillWeights function.

The function signature was changed in #8025a39d11.
Update AVR backend w.r.t API changes.

- TargetLowering constructor no longer wants a
TargetLoweringObjectFile*.
Instead, the getObjFileLowering() method has been added to
TargetMachine.

- setSupportJumpTables was removed.