flashmap and image generation: reduced union bcm_tag to a single struct...

flashmap and image generation: reduced union bcm_tag to a single struct combining the elements so that it is no longer necessary to create an openwrt-only tagid and tagcrc, and elimate the tagid detection and switch statements which made dealing with imagetags overly complicated, especially since the logic would need analogs in all code that touched the imagetag. Patch from cshore.

SVN-Revision: 20652