directfb: add options for divine and sawman

Since DirectFB 1.7.x, the divine (virtual input) and sawman (window
manager) features have been merged in DirectFB itself rather than
being shipped as separate tarballs. This commit creates additional
options to enable those features.

Upcoming commits will get rid of the existing divine and sawman
Buildroot packages.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>