clk: qcom: clk-rcg2: Fix DFS frequency table allocation

DFS controlled clock frequency table is allocated & updated when the
clock set rate is issued from the client driver. The end of frequency
table is marked with an extra zero-ed out entry, thus update the
allocation to take care of the same. While at it also add the ops to
list the supported rates for the DFS controlled clocks.

Change-Id: Ifad1014b69b83bf19d2bdba37a112f52b22da0a7
Signed-off-by: Taniya Das <tdas@codeaurora.org>