drm/amdgpu/sdma: allow caller to handle kernel rings in engine reset

Add a parameter to amdgpu_sdma_reset_engine() to let the
caller handle the kernel rings.  This allows the kernel
rings to back up their unprocessed state if the reset comes in
via the drm scheduler rather than KFD.

Reviewed-by: Jesse Zhang <Jesse.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>