drivers: clk: st: Add fs660c32 synthesizer algorithm

Use an algorithm instead of a table to compute clocks for fs660c32
synthesizer.
During a video playback we need to adjust audio & video frequencies.
A table can't cover all HDMI resolutions and audio adjustment.

Signed-off-by: Gabriel Fernandez <gabriel.fernandez@st.com>
Acked-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>