SPEAr: clk: Add Auxiliary Synthesizer clock

All SPEAr SoC's contain Auxiliary Synthesizers. Their Fout is derived based on
values of eq, x and y.

Fout from synthesizer can be given from two equations:
Fout1 = (Fin * X/Y)/2		EQ1
Fout2 = Fin * X/Y		EQ2

This patch adds in support for this type of clock.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Reviewed-by: Mike Turquette <mturquette@linaro.org>