st/dri: Always try to set up R5G6B5 configs.
Allows compiz to work in depth 16. The DRI2 getBuffersWithFormat hook is only required for 16/32 bit depth buffers, for colour buffers the only requirement is that the format matches the drawable depth, which we can't check here. (cherry picked from commit c50477c2)
Showing with 52 additions and 49 deletions