acpi: x86: Write FADT in common code

acpi: x86: Write FADT in common code

Write the FADT in common code since it's used on all architectures.
Since the FADT is mandatory all SoCs or mainboards must implement the
introduced function acpi_fill_fadt() and properly update the FADT.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Cc: Simon Glass <sjg@chromium.org>
Cc: Bin Meng <bmeng.cn@gmail.com>