Silicon/AMD/Styx: move XGBE declarations to separate SSDT table

Move the XGBE out of the DSDT, and along with it the logic that patches
the correct MAC address into the device nodes. However, this time we
patch the SSDT binary directly rather than relying on intermediate output
of an outdated version of the iasl compiler.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>