plat: marvell: armada: move mg conf related code to appropriate driver

Now when mg_conf_cm3 driver is present - move all relevant code there.

Change-Id: I444d9e877c450d6ee69ca3a49b547e4c3aeac0be
Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
4 files changed