bus: mvebu-mbus: Remove the no longer used name-based API

Now that every user of the deprecated name-based API has been
converted to using the ID-based API, let's remove the former one.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>