Following how it's done for the majority of drivers, add a new
VIDEO_EXYNOS option and Kconfig file under drivers/video/exynos and list
the current options there.

Cc: Anatolij Gustschin <agust@denx.de>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Minkyu Kang <mk7.kang@samsung.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Minkyu Kang <mk7.kang@samsung.com>