clk: qcom: clk-rcg2: Update logic to calculate D value for RCG

The current implementation does not check for D value is within
the accepted range for a given M & N value. Update the logic to
calculate the final D value based on the range. While at it, add
support for 2/3 divider in frac_table_pixel.

Change-Id: Ia42b9197de6d594129b1a48106f8e5a2be70a1c6
Signed-off-by: Taniya Das <tdas@codeaurora.org>
Signed-off-by: Jagadeesh Kona <jkona@codeaurora.org>