powerpc: Fix CMM page loaning on 64k page kernel with 4k hardware pages

If the firmware page size used for collaborative memory overcommit
is 4k, but the kernel is using 64k pages, the page loaning is currently
broken as it only marks the first 4k page of each 64k page as loaned.
This fixes this to iterate through each 4k page and mark them all as
loaned/active.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Robert Jennings <rcj@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>