video: da8xx-fb: store current display information

store current videomode and controller data so that reconfiguring can
be done easily. Reconfiguring would be required in fb_set_par, which
is going to be added soon.

If these details are not stored, the work probe does to retrieve these
information would have to repeated at the place of reconfiguring and
modifying platform data would be necessary to handle controller data
changes like bpp.

Signed-off-by: Afzal Mohammed <afzal@ti.com>
Signed-off-by: Darren Etheridge <detheridge@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>