drm/exynos: fimd: make a wait_for_vblank event to be handled in same period

drm/exynos: fimd: make a wait_for_vblank event to be handled in same period

This patch makes sure for a wait_for_vblank event to be handled
in same period. For this, it adds a new member, triggerred which
means whether trigger request is completed or not since trigger
request.

So if there is a trigger request, update-request, then this patch makes
a wait_for_vblank event to be handled after the trigger request is
completed.

Change-Id: If1a2491a323b637d20806373e0502b2b0a9ff810
Signed-off-by: Inki Dae <inki.dae@samsung.com>