Fix setting of workgroup size for `tile_to_foreach_thread_and_workgroup_count_region`  (#10673)

`tile_to_foreach_thread_and_workgroup_count_region` explicitly maps
dimensions to GPU thread blocks via attribute. This PR assigns workgroup
size according to given dimensions of `scf.foreach_thread`

Take a look at a 2D vectoradd example with 'linalg.generic' and
transform dialect.
```
linalg.generic {...} ins(%x: tensor<512x4xf32>) outs(%y: tensor<512x4xf32>) {...}
```
here is the transform dialect
```
transform.iree.tile_to_foreach_thread_and_workgroup_count_region %generic tile_sizes [4, 2] (
mapping = [#gpu.block<z>, #gpu.block<y>] )
```

Current iree launches the following which is wrong.
```
CUDA kernel <<< (gridDim.x=2, gridDim.y=128, gridDim.z=1), ...>>> -> Wrong!
```
This PR changes the kernel launch as below:
```
CUDA kernel <<< (gridDim.x=1, gridDim.y=2, gridDim.z=128), ...>>> -> Correct
```