pc: acpi: use build_append_foo() API to construct FADT

pc: acpi: use build_append_foo() API to construct FADT

build_append_foo() API doesn't need explicit endianness
conversions which eliminates a source of errors and
it makes build_fadt() look like declarative definition of
FADT table in ACPI spec, which makes it easy to review.
Also it allows easily extending FADT to support other
revisions which will be used by follow up patches
where build_fadt() will be reused for ARM target.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>