[media] exynos4-is: Compile in fimc runtime PM callbacks conditionally

Enclose the runtime PM helpers in #ifdef CONFIG_PM_RUNTIME/#endif
to avoid following compile warning when CONFIG_PM_RUNTIME is disabled:

 CC      drivers/media/platform/exynos4-is/fimc-core.o
drivers/media/platform/exynos4-is/fimc-core.c:1040:12: warning: ‘fimc_runtime_resume’ defined but not used
drivers/media/platform/exynos4-is/fimc-core.c:1057:12: warning: ‘fimc_runtime_suspend’ defined but not used

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>