clk: sunxi: unify APB1 clock

This commit unifies the APB1 mux with the APB1 clock, using the new
factors infrastructure.

Signed-off-by: Emilio López <emilio@elopez.com.ar>
[wens@csie.org: Add mux mask bits]
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>