clk: sunxi: rewrite sun6i-a31-ahb1-clk using factors clk with custom recalc

The factors clk implementation has been extended to support custom
recalc callbacks to support clocks that use one factor for certain
parents only, like a pre-divider.

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