hw/i386/acpi-build: move generic acpi building helpers into dedictated file

Move generic acpi building helpers into dedictated file and this
can be shared with other machines.

Signed-off-by: Shannon Zhao <zhaoshenglong@huawei.com>
Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>