driver: fix single-buffering
driver: solve flushing issues on gcwzero

- The rasterizer needs to wait for pixel engine after a clear
- Resolve must be flushed after copying to framebuffer
native: don't build egl directory by default

`egl` is only used for reverse engineering, and is not necessary
for using etnaviv.
Use 'make rev' to build the reverse-engineering only directories.
driver: move RS flush to more logical place
demos: remove dependency on GL headers

GLES/EGL headers were only used for data types. Use native types instead
to make it easier to build etnaviv for targets for which the rootfs
provides no GL headers.
Merge pull request #2 from laanwj/master

update to master