Silicon/AMD/StyxDtbLoaderLib: omit linux,phandle properties

The linux,phandle property is a deprecated alias for the phandle property
which was standardized long ago, so don't bother emitting it.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>