Add partitions/aix.h and partitions/aix.c.

AIX LVM permits to make "logical volumes" which are made of multiple
slices of multiple disks. The new code allows only access to the
"logical volumes" which are made of one slice on the probed disk, a
slice being a contiguous disk area. The code also detects "logical
volumes" made of multiple slices on the probed disk, but can not
describe them to the partition layer, because the partition layer
generic code does not support that. When such non-contiguous "logical
volumes" are detected, a diagnostic message is printed.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Philippe De Muyter
Cc: Karel Zak
Cc: Jens Axboe
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds