Reduce input arguments for `getPackingInfoFromConsumer` (NFC)

Pass to `getPackingInfoFromConsumer` the tensor.pack op instead of all
the arguments derived from it. Additionally, remove the padding from the
struct, as we currently don't handle propagation when `tensor.pack`
requires padding. We will add back the field when we will need it.

Reviewed By: hanchung

Differential Revision: https://reviews.llvm.org/D141837