drm/amdgpu: Enable userq fence interrupt support

Add support to handle the userqueue protected fence signal hardware
interrupt.

Create a xarray which maps the doorbell index to the fence driver address.
This would help to retrieve the fence driver information when an userq fence
interrupt is triggered. Firmware sends the doorbell offset value and
this info is compared with the queue's mqd doorbell offset value.
If they are same, we process the userq fence interrupt.

v1:(Christian):
  - use xa_load to extract the fence driver.
  - move the amdgpu_userq_fence_driver_process call within the xa_lock
    as there is a chance that fence_drv might be freed.

Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>