clk: sunxi: Implement A31 USB clock

clk: sunxi: Implement A31 USB clock

The A31 USB clock slightly differ from its older counterparts, mostly
because it has a different gate for each PHY, while the older one had
a single gate for all the phy.

Signed-off-by: Maxime Ripard <[email protected]>
Reviewed-by: Hans de Goede <[email protected]>
Acked-by: Mike Turquette <[email protected]>
Signed-off-by: Emilio López <[email protected]>