clk: sunxi: rewrite sun6i-ar100 using factors clk

sun6i's AR100 clock is a classic factors clk case:

AR100 = ((parent mux) >> p) / (m + 1)

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