dmm.cfg: Change dm-multipath from built-in kernel module to LKM

It is better to use LKM for dm-multipath.
1. For multipathd service, it will modprobe dm-multipath before
   start the daemon.
2. In package multipath, there is a script mpathconf which can
   config or check configuration of mutltipath, which will use
   lsmod to check if dm_multipath is loaded.

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>

cgl/cfg/dmm.cfg

-CONFIG_DM_MULTIPATH=y
+CONFIG_DM_MULTIPATH=m