video: cfb_console: add support for 4bpp bitmaps with GDF_32BIT_X888RGB

Add support for 4bpp bitmaps, currently only for GDF_32BIT_X888RGB
frame buffer format.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Anatolij Gustschin <agust@denx.de>