EXYNOS: Change bits per pixel value proper for u-boot.

vl_bpix of vidinfo_t was changed proper value for u-boot.
It is used to multiple of 2 by using NBITS() macro.

Signed-off-by: Donghwa Lee <dh09.lee@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>