A few types were missing: 8b/16b, signed/unsigned integers

Change-Id: I1c168b5df941f6c01801406ba7879221b682fb96
Reviewed-on: https://swiftshader-review.googlesource.com/7353Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>