ARM: DTS: keystone: complete the description of the USB PHY devices

As the PHY driver now handles the transitions of USB power domain, we
must add this information in the node of each PHY.
Also, the phy are expected in the "phys" property, not "usb-phys".
Also add the aliases for the USB ports on boards with more than a single
port.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>