- Add power of two flag to fractional divider clk type

* clk-frac-divider:
  clk: fractional-divider: Document the arithmetics used behind the code
  clk: fractional-divider: Introduce POWER_OF_TWO_PS flag
  clk: fractional-divider: Hide clk_fractional_divider_ops from wide audience
  clk: fractional-divider: Export approximation algorithm to the CCF users