clk: sunxi: Add USB clock register defintions

Add register definitions for the usb-clk register found on sun4i, sun5i and
sun7i SoCs.

Signed-off-by: Roman Byshko <rbyshko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Emilio López <emilio@elopez.com.ar>