Implement shader compiler support for uint scalars.

Bug 19331817

Change-Id: Ie901756ef4fdbab1dfa6ae01c77104fc84de247f
Reviewed-on: https://swiftshader-review.googlesource.com/2312
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>