Add support for quad primitives. Bug 18962347 Change-Id: Id13ef61a8aaacd88afb0b3e634ae971d44e39cd7 Reviewed-on: https://swiftshader-review.googlesource.com/1860 Reviewed-by: Nicolas Capens <capn@google.com> Tested-by: Nicolas Capens <capn@google.com>