video: exynos: Add a dependency to the menu

All drivers under menu EXYNOS_VIDEO depend on either ARCH_S5PV210 or
ARCH_EXYNOS, so add these as dependencies to the menu itself. This
avoids presenting an empty and useless menu on other architectures.

Then drivers under the menu only need a dependency if they depend on
one of the supported architectures specifically.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>