arm: zynq: Change OPP calculation

arm: zynq: Change OPP calculation

When the frequencies given in OPPs are converted to a frequency table
for the cpufreq driver, we lose three magnitudes of resolution, since
the CCF works with Hz and cpufreq with kHz frequencies.
Leverage the new 'clk_round_rate_nearest()' API function to calculate
OPP frequencies which should result in the intended actual frequency.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>