clk: sunxi: codec clock support

The codec clock on sun4i, sun5i and sun7i is a simple gate with PLL2 as
parent. Add a driver for such a clock.

Signed-off-by: Emilio López <emilio@elopez.com.ar>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>