OMAPDSS: Remove passive matrix LCD support (part 3)

Remove omap_lcd_display_type enum

The enum omap_lcd_display_type is used to configure the lcd display type in
DISPC. Remove this enum and always set display type to TFT by creating function
dss_mgr_set_lcd_type_tft().

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