drm/bridge: anx7625: add suspend / resume hooks

Add suspend / resume hooks for anx7625 driver, that power off the device
on suspend and power on the device on resume if it was previously
powered.

Signed-off-by: Pi-Hsun Shih <pihsun@chromium.org>
Reviewed-by: Tzung-Bi Shih <tzungbi@google.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210517063553.554955-2-pihsun@chromium.org