clk: sunxi-ng: Add common infrastructure

Start our new clock infrastructure by adding the registration code, common
structure and common code.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20160629190535.11855-3-maxime.ripard@free-electrons.com