drm/amdkfd: add proper handling for S0ix

drm/amdkfd: add proper handling for S0ix

commit 2ade36eaa9ac05e4913e9785df19c2cde8f912fb upstream.

When in S0i3, the GFX state is retained, so all we need to do
is stop the runlist so GFX can enter gfxoff.

Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Tested-by: David Perry <david.perry@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 4bfa8609934dbf39bbe6e75b4f971469384b50b1)
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>