Currently 32 bit unpacked offsets are passed as nxv2i64. However, as
pointed out in https://reviews.llvm.org/D71074, using nxv2i32 instead
would improve consistency with:
- how other arguments are treated
- how scatter stores are implemented
This patch makes sure that 32 bit unpacked offsets are passes as nxv2i32
instead of nxv2i64.