backends/drm,wayland: require gbm
The ifdefs for have_gbm obfuscate the code unnecessarily - the drm backend is not a great experience with qpainter, so in practice noone should ship it without gbm support anyways.
The ifdefs for have_gbm obfuscate the code unnecessarily - the drm backend is not a great experience with qpainter, so in practice noone should ship it without gbm support anyways.