clk: qcom: clk-rcg: Add a src_freq field to the RCG freq_tbl structure

We need to be able to specify the desired RCG parent frequency
in the RCGs frequency table for some clocks. Add a src_freq
field to hold that information.

Change-Id: I1f7fa1d4a7eda277bcd6770baa1f060e8454862b
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>