Silicon/AMD/Styx: merge ACPI table drivers

ACPI table support on Seattle is split into two parts for no good
reason: AcpiPlatformDxe and AmdStyxAcpiLib. Let's merge them
together, and clean up the code that iterates over the tables and
installs them.

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