Fixup cl_khr_command_buffer after spec unification (#1089)

After PR #950 merged the cl_khr_command_buffer spec needs
updated in a couple of places:

* Error around _num_queues_ to `clCreateCommandBufferKHR` should
  be in terms of `cl_khr_command_buffer_multi_device`.
* "New Structure" heading can be deleted as these are listed under
  "New Types"
* Typos in rendering of some types