PM: sleep: Call pm_sleep_fs_sync() instead of ksys_sync_helper()

PM: sleep: Call pm_sleep_fs_sync() instead of ksys_sync_helper()

Replace the direct calls to ksys_sync_helper() with the new
pm_sleep_fs_sync() in suspend and hibernation code paths.

This enables the new mechanism allowing the filesystem sync phase
to be interrupted.

Suggested-by: Saravana Kannan <saravanak@google.com>
Signed-off-by: Samuel Wu <wusamuel@google.com>
Co-developed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
[ rjw: Subject and changelog edits, tags adjustment ]
Link: https://patch.msgid.link/20251119171426.4086783-3-wusamuel@google.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>