drm/udl: implement usb_driver suspend/resume.

The usb_driver suspend and resume function pointers must be populated
to prevent forced unbinding of USB interface driver. See usb/core/driver.c:
unbind_no_pm_drivers_interfaces().

Restore mode and damage the entire frame buffer upon resume.

TEST=suspend and resume with the same UDL device connected
TEST=suspend with UDL, unplug UDL and resume
TEST=suspend with UDL, unplug and connect another UDL device then resume

Signed-off-by: Haixia Shi <hshi@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
[seanpaul fixed checkpatch warnings and gave marcheu his é back]
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1472593821-38429-2-git-send-email-hshi@chromium.org