[mlir][tosa] Remove optional for pad_const and remove input_zp attr for PadOp (#129336)
Always generated pad_const and remove input_zp attr for PadOp.
- Co-authored-by: Udaya Ranga <udaya.ranga@arm.com>
- Co-authored-by: Tai Ly <tai.ly@arm.com>
Signed-off-by: Jerry Ge <jerry.ge@arm.com>