qt5base: Qt KMS support does not depend on opengl

Qt KMS support should not explicitly depend on the availability of opengl.
Don't explicitly disable KMS if opengl is not available and fallback to
detecting if libdrm is available before disabling kms.

The scenario where this is necessary involves using the Qt linuxfb backend
"dumb buffer" support via the DRM API.  This is new in Qt 5.9 [1] and only
requires KMS, but not opengl. Although on Qt 5.6, only eglfs actually
uses libdrm/kms, it doesn't hurt to add the dependency and the -kms
option there as well, and doing so keeps the logic in the .mk file
simple.

[1] http://doc.qt.io/qt-5/embedded-linux.html#linuxfb



Cc: Peter Seiderer <ps.report@gmx.net>
Cc: Julien Corjon <corjon.j@ecagroup.com>
Signed-off-by: Joshua Henderson <joshua.henderson@microchip.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>