sh: cpufreq: Support CPU clock frequency table.

sh: cpufreq: Support CPU clock frequency table.

This adds support for the frequency table provided by the clock framework
under the struct clk definition (if available). In cases where no table
is generated or otherwise supported, we fall back on coarse grained
scaling via clock framework rounding, as before.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>