File _multibuild of Package optee-os

<multibuild>
  <flavor>armada3700</flavor>
  <flavor>armada7k8k</flavor>
  <flavor>hikey</flavor>
  <flavor>hikey960</flavor>
  <flavor>imx-mx6qsabrelite</flavor>
  <flavor>poplar</flavor>
  <flavor>qemu-armv7a</flavor>
  <flavor>qemu-armv8a</flavor>
  <flavor>rpi3</flavor>
</multibuild>