This continues the work on dot product instructions already started in
3cdac06.
This change adds support for all OpenCL integer dot product builtins
under `cl_khr_integer_dot_product` extension, namely:
```
* dot
* dot_acc_sat
* dot_4x8packed_(uu/ss/su/us)_(u)int
* dot_acc_sat_4x8packed_(uu/ss/su/us)_(u)int
```