drm/bridge: parade-ps8640: Link device to ensure suspend/resume order

drm/bridge: parade-ps8640: Link device to ensure suspend/resume order

Entering suspend while the display attached to this bridge is still on
makes the resume sequence to resume the bridge first, display last:
when this happens, we get a timeout while resuming the bridge, as its
MCU will get stuck due to the display being unpowered.

On the other hand, on mt8173-elm, closing the lid makes the display to
get powered off first, bridge last, so at resume time the sequence is
swapped (compared to the first example) and everything just works
as expected.

Add a stateless device link to the DRM device that this bridge belongs
to, ensuring a correct resume sequence and solving the unability to
correctly resume bridge operation in the first mentioned example.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220105090802.73564-1-angelogioacchino.delregno@collabora.com
Reviewed-by: Robert Foss <robert.foss@linaro.org>