OMAPDSS: Add N800 panel driver

This is a driver for N800's display, ported from the old omapfb. This is
a slightly lighter version of the driver as not all features of the old
driver can be ported without big changes to DSS2, and also because some
of the HW features used in the old driver are unclear (e.g. the power
management part).

That said, the new driver works fine for basic use.

Architecturally the driver is not as neat as it could be. N800's display
HW consists of a display buffer chip and a panel, and ideally they would
be represented by separate, independent drivers. This is not currently
possible, and this driver contains both buffer chip and panel driver.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>