directfb: Include directfbgl.h directly

directfb: Include directfbgl.h directly

directfb.h is included directly in all other files, include
directfbgl.h without the directfb/ prefix as well.

$ pkg-config --cflags directfb
-D_REENTRANT -I/home/foo/install/directfb/include/directfb

Merge-request: 2643
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>
(cherry picked from commit 647ffa677f9bf6da50fcdb7a6948501e7e6719ce)

Change-Id: If96f378a95e7790132e89f934341977520367018
Reviewed-on: http://codereview.qt-project.org/4579
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>