mm: MEMF_node should handle changes in nodeid_t size

mm: MEMF_node should handle changes in nodeid_t size

Instead of using a hardcoded constant to extract nodeID from
memflags use a macro whose value is based on nodeid_t size.

Also provide a macro for extracting nodeID from memflags so that
users don't need to remember to decrement the value.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
MASK_EXTR() can't be used in MEMF2NODE() (also renamed to
MEMF_get_node()).

Signed-off-by: Jan Beulich <jbeulich@suse.com>