To start with this backend only supports creating a single CoglOnscreen
framebuffer and will automatically set is up to display fullscreen on
the first suitable crtc it can find.
To compile this backend - get some dribbly black candles, sacrifice a
goat and configure with: --enable-kms-egl-platform
Note: There is currently a problem with using GLES2 with this winsys
so you need to run with EGL_DRIVER=gl
Note: If you have problems with mesa crashing in XCB during
eglInitialize then you may need to explicitly run with EGL_PLATFORM=gbm
Reviewed-by: Robert Bragg <robert@linux.intel.com>
1b54c8023e