USB: add ehci-ppc-of bus glue (device-tree aware)

This adds device-tree-aware ehci-ppc-of driver.
The code is based on the ehci-ppc-soc driver by
Stefan Roese <sr@denx.de>.

Signed-off-by: Valentine Barshak <vbarshak@ru.mvista.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Stefan Roese <sr@denx.de>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>