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>
This is a bashism. While we don't necessarily allow the user's shell to be dash, still I think we should avoid non-portable constructs in a shell script that gets sourced into whatever shell the user happens to be using :)

This would probably do:
```
case "$SETUP_ENV_MACHINE" in
    qemu*)
        # do stuff
        ;;
esac
```