Lyude+tomeu's changes: new kernel ABI, no more slowfb, actual winsys
Here comes the big one....
Upgrade the kernel ABI to work with Arm's latest driver. A compatible kernel module can be found at tomeu/mali_kbase, for instance. This breaks older kernels, but fixes newer ones, so hey. Thanks @lyudess!
Replace Xshm-based slowfb with an actual, honest-to-goodness winsys. At the moment, this only works from raw DRM, but most of the apps we test on (glmark, Weston, mpv) have DRM backends, which are confirmed working. This breaks trying to run from X11, but... that was -already broken- so I can't feel too bad now, can I? Thanks @tomeu!
Other assorted changes, mostly working towards the above. Read the log yourself, hehe.