32-bit integer vertex attribute

Added 32-bit signed and unsigned vertex attribute

Change-Id: Ibbf9c035294584db71713ae7aeca36b32a8564c0
Reviewed-on: https://swiftshader-review.googlesource.com/4974
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>