RGB_565 is now as fast if not faster than 32-bit formats.

Change-Id: I6358e35557164541601ac76ae11028afba439084
Reviewed-on: https://swiftshader-review.googlesource.com/4253Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>