Revert an earlier change to SIGN_EXTEND_INREG for vectors. The VTSDNode

Revert an earlier change to SIGN_EXTEND_INREG for vectors. The VTSDNode
really does need to be a vector type, because
TargetLowering::getOperationAction for SIGN_EXTEND_INREG uses that type,
and it needs to be able to distinguish between vectors and scalars.

Also, fix some more issues with legalization of vector casts.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93043 91177308-0d34-0410-b5e6-96231b3b80d8