drm/amdgpu: UAPI for user queue management

This patch intorduces new UAPI/IOCTL for usermode graphics
queue. The userspace app will fill this structure and request
the graphics driver to add a graphics work queue for it. The
output of this UAPI is a queue id.

This UAPI maps the queue into GPU, so the graphics app can start
submitting work to the queue as soon as the call returns.

V2: Addressed review comments from Alex and Christian
    - Make the doorbell offset's comment clearer
    - Change the output parameter name to queue_id

V3: Integration with doorbell manager

V4:
    - Updated the UAPI doc (Pierre-Eric)
    - Created a Union for engine specific MQDs (Alex)
    - Added Christian's R-B
V5:
    - Add variables for GDS and CSA in MQD structure (Alex)
    - Make MQD data a ptr-size pair instead of union (Alex)

V9:
   - renamed struct drm_amdgpu_userq_mqd_gfx_v11 to struct
     drm_amdgpu_userq_mqd as its being used for SDMA and
     compute queues as well

V10:
    - keeping the drm_amdgpu_userq_mqd IP independent, moving the
      _gfx_v11 objects in a separate structure in other patch.
      (Alex)

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian Koenig <christian.koenig@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Shashank Sharma <shashank.sharma@amd.com>