[SCSI] isci: add CONFIG_PM_SLEEP to suspend/resume functions

Add CONFIG_PM_SLEEP to suspend/resume functions to fix the following
build warning when CONFIG_PM_SLEEP is not selected. This is because
sleep PM callbacks defined by SIMPLE_DEV_PM_OPS are only used when
the CONFIG_PM_SLEEP is enabled.

drivers/scsi/isci/init.c:725:12: warning: 'isci_suspend' defined but not used [-Wunused-function]
drivers/scsi/isci/init.c:743:12: warning: 'isci_resume' defined but not used [-Wunused-function]

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Lukasz Dorau <lukasz.dorau@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>