MLK-22309-1 media: mxc-parallel-csi: mark PM functions as __maybe_unused

MLK-22309-1 media: mxc-parallel-csi: mark PM functions as __maybe_unused

fix build warnings if CONFIG_PM_SLEEP is disabled.

drivers/media/platform/imx8/mxc-parallel-csi.c:618:12: warning: 'parallel_csi_pm_resume' defined but not used [-Wunused-function]
 static int parallel_csi_pm_resume(struct device *dev)
            ^~~~~~~~~~~~~~~~~~~~~~
drivers/media/platform/imx8/mxc-parallel-csi.c:613:12: warning: 'parallel_csi_pm_suspend' defined but not used [-Wunused-function]
 static int parallel_csi_pm_suspend(struct device *dev)
            ^~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Robby Cai <robby.cai@nxp.com>
Reviewed-by: Sandor Yu <Sandor.yu@nxp.com>