Were the changes you made to my code really necessary?  AFAICT, you
introduced two bugs:

1) The region used by the kernel was already eliminated from the map
   by putting it in mem_clusters[0] and not probing it.  Your adjust
   of mem_clusters[1].size will simply remove the same amount of
   memory from the *end* of DRAM bank 0, thereby wasting memory.

2) You removed the possibility of supporting 32MB cards by requiring
   that there be a `mirror' page.  The test to make sure that the
   magic values could be reread should have been sufficient to insure
   that we detect the lack of a memory card.