USB: bcma: initialize Northstar USB 3.0 controller

It's a rather simple controller, we just need to make sure USB is
powered (using GPIO pin) and reset bus core. Once this is done it's
safe to register XHCI controller and let it init PHY and do its magic.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>