clk: sunxi: Add A31 clocks support

The A31 has a mostly different clock set compared to the other older
SoCs currently supported in the Allwinner clock driver.

Add support for the basic useful clocks. The other ones will come in
eventually.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Emilio López <emilio@elopez.com.ar>