clk: qcom: Update the display port determine rate RCG ops

The display port PLL generates only limited set of frequency combinations.
As fractional dividers are not required to be used, update the RCG ops to
take care of the same.

Change-Id: I601273fee044ef128dbc7c2e23bc2d8ce10e31dc
Signed-off-by: Taniya Das <tdas@codeaurora.org>