ieee1275: Drop len -= 1 quirk in heap_init

ieee1275: Drop len -= 1 quirk in heap_init

This was apparently "required by some firmware": commit dc9468500919
(2007-02-12  Hollis Blanchard  <hollis@penguinppc.org>).

It's not clear what firmware that was, and what platform from 14 years ago
which exhibited the bug then is still both in use and buggy now.

It doesn't cause issues on qemu (mac99 or pseries) or under PFW for Power8.

I don't have access to old Mac hardware, but if anyone feels especially
strongly we can put it under some feature flag. I really want to disable
it under pseries because it will mess with region merging.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Tested-by: Nageswara R Sastry <rnsastry@linux.ibm.com>
Reviewed-by: Robbie Harwood <rharwood@redhat.com>