862a1bea6f
This patch makes sure that in the absence of an explicit pad value in `linalg.pack`, the vectorizer will use `ub.poison` for the corresponding Xfer Op pad value (as opposed to e.g. `arith.constant 0`). Also, in the case of `linalg.unpack`, use `ub.poison` for the Xfer read operation. In this case, there is no mechanism for a user to specify the pad/pass-thru value.