Add a PCD to allow the platform to mask in/out specific features of the LAN9118 device advertised during auto-negotiation. For example, the Juno ARM Development Platform doesn't support full duplex mode. This PCD will allow the platform developer to prevent the full duplex modes from being advertised. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Ryan Harkin <ryan.harkin@linaro.org> [ardb: change default feature mask so that full duplex is disabled] Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Acked-by: Leif Lindholm <leif.lindholm@linaro.org>