atags_to_fdt: Propagate ATAG_REVISION to the fdt
The ATAGS have various tags useful to determine platform specific data already aquired or directly coming from the bootloader. In this case it is the revision tag that the bootloader might fill in ghe ATAGS structure.
To be able to handle this later after teh ATAHS are destroyed parse the ATAG_REVISION and add it to a atag-revision entry in teh device tree.
In the G&F case and using the Flash-N-Go Boot bootloader the bootloader version is propagated in the ATAGS_REVISION tag.
Change-Id: I5a358e3113e30cc7f13b5c328fba42f01df72a70