clk: fractional-divider: Introduce POWER_OF_TWO_PS flag

The newly introduced POWER_OF_TWO_PS flag, when set, makes the flow
to skip the assumption that the caller will use an additional 2^scale
prescaler to get the desired clock rate.

Reported-by: Liu Ying <victor.liu@nxp.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210812170025.67074-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>