Deduplicate common functions and remove unsized color buffer formats.

Change-Id: I76b3b507c27c8bfa932aab64a9338e2a124a25da
Reviewed-on: https://swiftshader-review.googlesource.com/16289Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>