ARM: imx25: set default phy_type and dr_mode for usbotg port
All currently supported i.MX25-based machines use phy_type = "utmi" and
dr_mode = "otg". So this seems to be a sensible default.
This also doesn't hurt out-of-tree machines because up to now they had
to specify these two properties in the machine.dts which still takes
precedence by just overwriting the defaults added here.