video: da8xx-fb: fix 24bpp raster configuration

Based on original patch by: Manjunathappa, Prakash <prakash.pm@ti.com>
	and Afzal Mohammed <afzal@ti.com>

Set only LCD_V2_TFT_24BPP_MODE bit for 24bpp and LCD_V2_TFT_24BPP_UNPACK
bit along with LCD_V2_TFT_24BPP_MODE for 32bpp configuration.

Patch is tested on am335x-evm for 24bpp and da850-evm for 16bpp
configurations.

v2: removes confusing fall through in case statement for pixel
	depth configuration.

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