OMAPDSS: Taal: Reogranize for device tree

Reorganize taal driver to make it easier to integrate device tree code.
Instead of storing the panel's platform data, we'll "parse" the platform
data and store the required information in driver's own data. This way
adding device tree data parsing is simple.

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