[media] exynos4_is: exynos4-fimc requires i2c

Without i2c, we can get a build error:

drivers/media/platform/exynos4-is/fimc-is-i2c.c: In function 'fimc_is_i2c_probe':
drivers/media/platform/exynos4-is/fimc-is-i2c.c:58:8: error: implicit declaration of function 'i2c_add_adapter' [-Werror=implicit-function-declaration]

The dependency already exists for exynos-fimc-lite and s5p-fimc,
but is missing for exynos4-fimc.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>