The old_fb field is only used to indicate whether a page flip is
pending. Turn it into a bool named flip_pending. Rename event and
page_flip_work to flip_event and flip_work for consistency.
Signed-off-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>