IB/core: Move CM_xxx_ATTR_ID macros from cm_msgs.h to ib_cm.h

These macros will be reused by the mlx4 SRIOV-IB CM paravirtualization
code, and there is no reason to have them declared both in the IB core
in the mlx4 IB driver.

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>