[media] exynos4-is: Remove dependency on SYSCON for non-dt platforms

Currently the whole driver depends on MFD_SYSCON, which in turn
depends on OF. To allow to use the driver on non-dt platforms
(S5PV210) the SYSREG support is made conditional (it is needed
only for dt enabled platforms) and MFD_SYSCON is selected if
OF is enabled, instead of depending on OF.

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