[media] exynos4-is: add of_platform_populate() call for FIMC-IS child devices

[media] exynos4-is: add of_platform_populate() call for FIMC-IS child devices

Instead of relying on the "simple-bus" compatible and the driver core
populating FIMC-IS child devices make the fimc-is driver populating
its child devices.  This prevents issues related to accessing ISP_I2C
clock registers with corresponding power domain switched off, which
popped out after applying some pending IOMMU driver patches.  Now the
I2C_ISP child devices will be instantiated only when required parent
device drivers are initialized and ready.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>