[ARM] 5164/1: pxafb: Support for RGB666, RGBT666, RGB888 and RGBT888

Add the .depth field to pxafb_mode_info and use it to set pixel data format
as 18(RGB666), 19(RGBT666), 24(RGB888) or 25(RGBT888)

Signed-off-by: Daniel Ribeiro <drwyrm@gmail.com>
Acked-by: Eric Miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>