directfb: Convert the directfb plugin, disable the OpenGL support

directfb: Convert the directfb plugin, disable the OpenGL support

OpenGL was never tested and the platform integration has changed,
remove it from the build and re-enable it once one can test it.

Change-Id: I70d5b5b11de06e6e999d3aae44660f11d2dbc719
Reviewed-on: http://codereview.qt.nokia.com/3666
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>