Add boot animation preview (1/2)

This change is needed to get notified once the animation is finished.
The usecase would be multipart animations where the first part is shown
once and the second is shown in a loop.

Change-Id: Ibd9c83a4662bef2a866c5bb076d94f49e714dd63
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>