usb: phy: Add interface to get phy give of device_node.

Split the "get phy from device_node" functionality out of
"get phy by phandle" so it can be used directly.

This is useful when a battery-charger is intimately associated with a
particular phy but handled by a separate driver.  The charger
can find the device_node based on sibling relationships
without the need for a redundant declaration in the devicetree
description.

As a peripheral that gets a phy will often want to register a
notifier block, and de-register it later, that functionality
is included so the de-registration is automatic.

Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>