mlx4_core: Allow large mlx4_buddy bitmaps

mlx4_buddy_init uses kmalloc() to allocate bitmaps, which fails when
the required size is beyond the max supported value (or when memory is
too fragmented to handle a huge allocation).  Extend this to use use
vmalloc() if kmalloc() fails, and take that into account when freeing
the bitmaps as well.

This fixes a driver load failure when log num mtt is 26 or higher, and
is a step in the direction of allowing to register huge amounts of
memory on large memory systems.

Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>