ACPICA: FADT support cleanup

ACPICA commit 34ccd43af3fd1870fddfac0617dd0ba706963558

Remove all vestiges of the version 2 FADT which never was included
in the ACPI specification.

This enabled significant cleanup of both the data table compiler
and the disassembler.

Added many clarification comments to associate each FADT version
with the version of the ACPI spec where it was originally
defined.

Link: https://github.com/acpica/acpica/commit/34ccd43a


Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>