[PATCH] powerpc: Auto reserve of device tree blob

A devtree compiler (dtc) generated devtree blob is "relocatable" and so
does not contain a reserved_map entry for the blob itself.  This means
that if passed to Linux, Linux will not get lmb_reserve() the blob and
it could be over.  The following patch will explicitly reserve the
"blob" as it was given to us and stops prom_init.c from creating a
reserved mapping for the blob.

NOTE: that the dtc/kexec should not generate the blob reservation entry.
Although if they do, LMB reserver handles overlaps.

Signed-off-by:  <jimix@watson.ibm.com>
Acked-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>