qt4-webos: explicitly disable opengl for x86

* mesa is now autodetected in some builds

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: Iab213a5ab5ffefeb6790891b4f877983007faa9f
Reviewed-on: https://g2g.palm.com/1888
Reviewed-by: Susan Montooth <susan.montooth@lge.com>
Tested-by: Susan Montooth <susan.montooth@lge.com>