Show firmware provided stackpointer during boot.

This helps to find the "taboo" areas on the various boards.  claim tends to
fail for these memory areas, but some jokers return success anyway.

Use %p to print the load address, its a pointer.
Signed-off-by: Olaf Hering <olh@suse.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Anton Blanchard <anton@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>