tegra: Fill in some details

Implement DRM buffer object handling and add support for clearing a
buffer. This allows a very basic OpenGL ES program, calling glClear(),
to run.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
tegra: remove non-existent cap
tegra: format clean-up
tegra: use linear staging-textures
tegra: round up height to multiples of tile-size
tegra: perform blits with gr2d
tegra: implement fences
tegra: perform transfers with blits
tegra: clean up clear cmdstream
tegra: reduce printfs
tegra: clean up blit-code
tegra: non-fullscreen clears
tegra: get rid of bpp
tegra: only align 2d-resources
tegra: comment blit-cmdstream a bit more
tegra: do not crash on NULL vertex-state object
tegra: no more user buffers
tegra: add missing blocksize-cases to clear-code
tegra: clarify clearing-code a bit
tegra: add comments for regsiter names in clear