drm/amdgpu: Add handler for SDMA context empty

Context empty interrupt is enabled for SDMA 4.4.2. Add a handler for
context empty interrupt so that it is disposed of fast, and not
propagated to KFD layer.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Suggested-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>