clk: sunxi: Add a common setup function for mmc module clocks

The only difference between module clocks on different platforms is the
width of the mux register bits and the valid values, which are passed in
through struct factors_data. The phase clocks parts are identical.

This patch generalizes the setup function, so most of the code can be
reused when adding sun9i support, which has a wider mux register.

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