Platform: add acpiview to Seattle/Styx platforms

Enable the 'acpiview' UEFI shell command so we can inspect the ACPI
tables at boot time.

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