video: da8xx-fb: adding am33xx as dependency

Updating Kconfig to allow am33xx to include lcdc fbdev driver
including some extra dependencies needed by device tree mods.

v2: must add FB_MODE_HELPERS as VIDEOMODE_HELPERS alone doesn't
	get the correct functions from fbmon.c built in.

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