[media] s5p-fimc: Only build suspend/resume for PM

If power management is disabled these functions become unused, so there
is no reason to build them. This fixes a couple of build warnings when
PM(_SLEEP,_RUNTIME) is not enabled.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>