drm/amdgpu: Fix Illegal opcode in command stream Error

When applications closes, it triggers the drm_file_free
function which subsequently releases all allocated buffer
objects. Concurrently, the resume_worker thread will attempt
to map the usermode queue. However, since the wptr buffer
object has already been deallocated, this will result in
an Illegal opcode error being raised in the command stream.

Now replacing drm_release() with a new function
amdgpu_drm_release(). This function will set the flag to
prevent the scheduling of any new queue resume/map, stop
all queues and then call drm_release().

V2:
  - Replace drm_release with amdgpu_drm_release(Christian).

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian Koenig <christian.koenig@amd.com>
Reviewed-by: Shashank Sharma <shashank.sharma@amd.com>
Signed-off-by: Arvind Yadav <arvind.yadav@amd.com>
Change-Id: I7fec40c02a2d20c4ff3cd38d7760545d0b0b2f9c