clk: sunxi-ng: Add M-P factor clock support

Introduce support for the clocks that combine a linear divider and a
power-of-two based one.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20160629190535.11855-9-maxime.ripard@free-electrons.com