[MLIR] tosa.rescale op validation incorrectly fails on unsigned integer type

[samvid25]

See godbolt: https://godbolt.org/z/8z6Ycahnv
According to the TOSA Spec (here), unsigned 8 and 16-bit types are allowed in the RESCALE operation. The TOSA dialect docs specify the same as well (here).

[llvmbot]

@llvm/issue-subscribers-mlir

Author: Samvid Dharanikota (samvid25)

See godbolt: https://godbolt.org/z/8z6Ycahnv According to the TOSA Spec ([here](https://www.mlplatform.org/tosa/tosa_spec.html#_integer_behavior)), unsigned 8 and 16-bit types are allowed in the RESCALE operation. The TOSA dialect docs specify the same as well ([here](https://github.com/llvm/llvm-project/blob/76db259080fa134579f31d76fe9ab462f47eca87/mlir/include/mlir/Dialect/Tosa/IR/TosaOps.td#L2360)).