Since tosa.pad is lowered strictly to artih and tensor ops, move ConvertPad from TosaToLinalg to TosaToTensor, benefitting non-Linalg Tosa targets. TensorToLinalg exists, and is trivial, so nothing is lost. Signed-off-by: Ramkumar Ramachandra <r@artagnon.com> Differential Revision: https://reviews.llvm.org/D139091