Implement auto-update mode for manual-update displays. omapfb driver
uses a delayed work to update the display with a constant rate.

The update mode can be changed via OMAPFB_SET_UPDATE_MODE ioctl, which
previously called omapdss but is now handled inside omapfb, and a new
sysfs file, "update_mode".

The update interval is by default 20 times per second, but can be
changed via "auto_update_freq" module parameter. There is also a new
module parameter "auto_update", which will make omapfb start manual
update displays in auto-update mode.

This auto-update mode can be used for testing if the userspace does not
support manual update displays properly. However, it is a very
inefficient solution, and should be considered more as a hack for
testing than something that could be used as a long term solution.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>