OMAPDSS: RFBI: Maintain copy of number of data lines in driver data

The RFBI driver currently relies on the omap_dss_device struct to configure the
number of data lines as specified by the panel. This makes the RFBI interface
driver dependent on the omap_dss_device struct.

Make the RFBI driver data maintain it's own data lines field. A panel driver
is expected to call omapdss_rfbi_set_data_lines() to configure the pixel format
before enabling the interface or calling omap_rfbi_configure().

Signed-off-by: Archit Taneja <archit@ti.com>