This avoids race conditions in GL drivers when attempting to render and
call glEGLImageTargetTexture2DOES on the same texture.
Also, when using glEGLImageTargetTexture2DOES, we do not need to allocate
storage for textures.
The way things were handled in EGLTexture is not only very hard to
follow, but broken. This change set breaks up EGLTexture into a modular
design making it easier to implement the various versions.
Note that DMABUF is currently broken and needs to be re-implemented.