Extend the clock controller module with a function to calculate
core clocks from the current registers settings. On Vybrid, we
assume that the core clocks are setup by the main operating system
running on the Cortex-A5. Nevertheless we need to know their actual
values in order to calculate other clocks or baud rates.
Verified on a Colibri VF61, which calculates following values:
ccm_core_clk: 500210526
ccm_platform_bus_clk: 166736842
ccm_ipg_bus_clk: 83368421
