Silicon/AMD/Styx/AcpiPlatformDxe: disable KCS on pre-B1 silicon

Align the ACPI platform driver with the DT patching code, which only
enables the IPMI/KCS device node on B1 silicon (or later).

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