[media] exynos-gsc: remove non-device-tree init code

Exynos platform has been fully converted to device tree,
so old platform device based init data can be now removed.

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@osg.samsung.com>