drm/amdgpu: Add APTX quirk for Dell Latitude 5495

commit 317a3aaef94d73ba6be88aea11b41bb631b2d581 upstream.

Needs ATPX rather than _PR3 to really turn off the dGPU. This can save
~5W when dGPU is runtime-suspended.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>