Mem-free mode requires the driver to allocate additional doorbell pages
for each user access region.  Add support for this in mthca_memfree.c,
and have the driver allocate a table in db_tab for kernel use.
Signed-off-by: Roland Dreier <roland@topspin.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>