clk: Add support to provide OPP tables for clocks

Some clock driver clients need the frequency to voltage
mapping to be exposed. Add support to load and expose
these values through OPP tables.

Change-Id: I6305c44411eb591fc0d337187079d8d881135a64
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>