ARM: Dove: convert usb host controller to DT

With DT support for orion-ehci also convert Dove to it and
remove the legacy calls and clock aliases.

This patch is based on "ARM: Dove: split legacy and DT setup"
applied to mvebu/boards recently.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>