ov5645: Add support for 'unzoomed' 1080p@15fps

1080p@30fps simply crops the full 5M image, thus looking
like a zoomed version of 5M. 1080p@15fps solves the zoom
issue by sampling over the full 5M image. This has however
has performance releated side effects, and hence the 15fps.

Change-Id: Iba30abff17692e85df20d35f61d6347c7796db2b