Texturing and shadow map example broken with Radeon

When running with a Radeon HD7500 card on Linux with the AMD proprietary driver 14.20, supporting up to OpenGL 4.4, the following issues popped up:

• Textures are broken in examples like materials and skybox. This is due to the DSA code path in QOpenGLTexture. When disabling the DSA code path, the examples start rendering correctly.

• The shadow map example does not render the materials correctly. The objects like the airplane are all gray.