[media] exynos4-is: Remove support for non-dt platforms

All platforms supported by this driver are going to get device tree
support in this kernel release so remove code that would have been
actually not used any more.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>