clk: sunxi-ng: Add divider

Add support for the various dividers (linear, table or pow-of-two based)
found in the CCU.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20160629190535.11855-8-maxime.ripard@free-electrons.com