[DAGCombine] Initialize the default operation action for SIGN_EXTEND_INREG for...

[DAGCombine] Initialize the default operation action for SIGN_EXTEND_INREG for vector type as 'expand' instead of 'legal'

For now, we didn't set the default operation action for SIGN_EXTEND_INREG for
vector type, which is 0 by default, that is legal. However, most target didn't
have native instructions to support this opcode. It should be set as expand by
default, as what we did for ANY_EXTEND_VECTOR_INREG.

Differential Revision: https://reviews.llvm.org/D70000