[media] exynos4-is: Staticize local symbols

These symbols are used only in their respective files and hence
should be made static.
[s.nawrocki@samsung.com: dropped the __fimc_is_hw_update_param()
 function change]

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>