Silicon/AMD/Styx/AcpiPlatformDxe: move IPMI/KCS device into separate SSDT

Move the IPMI/KCS device node from the DSDT into its own SSDT, and only
install it if we have support for KCS enabled in the platform.

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