setup-environment: Add sdl PACKAGECONFIG for qemu-native.

* Add PACKAGECONFIG for qemu-native for qemu machines. Get the machine
  name and added when its one of the qemu machine.

Signed-off-by: Noor Ahsan <noor_ahsan@mentor.com>
I think we might want to clarify that these lines add a dependency on SDL on their host / build machine, here.