clk: sunxi-ng: Add phase clock support

Add support for the clocks in the CCU that introduce a phase shift from
their parent clock.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20160629190535.11855-7-maxime.ripard@free-electrons.com