clk: sunxi-ng: Add minimums for all the relevant structures and clocks

Modify the current clocks we have to be able to specify the minimum for
each clocks we support, just like we support the max.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>