Add exynos video driver

Documentation is provided in README-exynos.
Remove the lima video driver

The driver is now superseded by the exynos video driver. Also limare
only works up to mali kernelspace driver version r3p2, which makes
the driver nonfunctional with the latest r4p0.
exynos: adapt to video_driver interface changes

The restart API was removed.
exynos: adapt to naming changes

The RGUI is now just called 'menu'.
exynos: adapt font rendering code
exynos: fix typo in comment
exynos: disable crtc before freeing buffers

The crtc should be disabled before deallocating the buffers, otherwise
leading to a use-after-free scenario, which can trigger all sorts
of funny effects.
Merge pull request #817 from tobiasjakobi/exynos

Exynos video driver