Native bindings to the MESA_bgra extension.

MESA_bgra extends the list of combinations host-memory color formats with internal formats to include BGRA and BGR as acceptable formats with RGB8/SRGB8 and RGBA/sRGB8_ALPHA8 as internal formats respectively. This feature is of interest in virtualized environments, where the host supports OpenGL ES only, and the virtualized guest is supposed to support a subset of OpenGL including textures created with the format BGRA.