drm/amdgpu: Add work_struct for GPU reset from kfd.

We need to have a work_struct to cancel this reset if another
already in progress.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>