ppc/km: enable DM driver support in all defconfigs

This is the first step to use DM support for the KM powerpc boards.

Signed-off-by: Holger Brunck <holger.brunck@ch.abb.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
CC: Mario Six <mario.six@gdsys.cc>
CC: Wolfgang Denk <wd@denx.de>
CC: Valentin Longchamp <valentin.longchamp@ch.abb.com>
CC: Priyanka Jain <priyanka.jain@nxp.com>