OMAPDSS: Remove passive matrix LCD support (part 2)

Remove OMAP_DSS_LCD_TFT as a omap_panel_config flag.

We don't support passive matrix displays any more. Remove this flag from all the
panel drivers.

Force the display_type to OMAP_DSS_LCD_DISPLAY_TFT in the interface drivers.

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