Silicon/AMD/Styx: emit DSDT as aml directly

Instead of emitting the DSDT by incorporating the intermediate output
of [some version of] the iasl compiler, move the DSDT source file to
the ACPI platform driver, which will install it directly. This permits
us to drop a lot of cruft related to handling of this intermediate
output.

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