drm/bridge: analogix_dp: Enable autosuspend

DP AUX transactions can consist of many short operations. There's no
need to power things up/down in short intervals.

I pick an arbitrary 100ms; for the systems I'm testing (Rockchip
RK3399), runtime-PM transitions only take a few microseconds.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220301181107.v4.2.I48b18ab197c9b649d376cf8cfd934e59d338f86d@changeid