[SelectionDAG][RISCV] Use VP_LOAD to widen MLOAD in type legalization when possible. (#140595)
Padding the mask using 0 elements doesn't work for scalable vectors. Use
VP_LOAD and change the VL instead.
This fixes crash for Zve32x. Test file was split since i64 isn't a valid
element type for Zve32x.
Fixes #140198.