Implement R5G6B5 framebuffer present. Bug 20891368 Change-Id: If4b0b84d141eb16c96600b7ade98a552e5f2ad0e Reviewed-on: https://swiftshader-review.googlesource.com/3251 Reviewed-by: Nicolas Capens <capn@google.com> Tested-by: Nicolas Capens <capn@google.com>