[NVPTX] Set v2i16 SETCC to Expand (#108969)
Note that this refers to the return type of SETCC. This operation is not
legal in PTX but was assumed as such because v2i16 is declared a legal
type. We were already expanding v4i8 SETCC.
The DAGCombiner would in certain circumstances try to fold an extension
of an illegal v2i1 SETCC (because v2i1 is illegal) into a "legal" v2i16
SETCC, which we wouldn't have patterns for.
