sunxi: usb: Protect phy-init and phy-power-on against multiple calls

Once we add support for the ohci controller the phy-init and phy-power-on
functions may be called twice (once by the ehci code and once by the ohci
code) protect them against this.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>