SelectionDAG: Expand SELECT_CC to SELECT + SETCC

This consolidates code from the Hexagon, R600, and XCore targets.

No functionality change intended.
SelectionDAG: Enable (and (setcc x), (setcc y)) -> (setcc (and x, y)) for vectors

This prevents a future commit from regressing:

test/CodeGen/R600/setcc-equivalent.ll
SelectionDAG: Don't use MVT::Other to determine legality of ISD::SELECT_CC

The SelectionDAG bad a special case for ISD::SELECT_CC, where it would
allow targets to specify:

setOperationAction(ISD::SELECT_CC, MVT::Other, Expand);

to indicate that they wanted to expand ISD::SELECT_CC for all types.
This wasn't applied correctly everywhere, and it makes writing new
DAG patterns with ISD::SELECT_CC difficult.