[mlir][tosa] Allow shift operand of tosa::MulOp as non-constant (#155197)
The shift operand of tosa::MulOp could be non-constant when the dynamic
extension enabled. Given that checkConstantOperandMul could check the
shift operand according to the extension, we might able to relax the
checking in TosaToLinalg.
Relative discussion:
https://discourse.llvm.org/t/tosa-ext-dynamic-clearification-needed/87478?u=r2333333.