clk: Add support to vote to regulator framework from clk framework

Add vdd_class support which would help vote/unvote for any voltage rail
for the clock frequency to the regulator framework. A clock client request
for a clock frequency would look for the corresponding voltage vote and
would be send the request to regulator framework.

Change-Id: I5b1229091fcb7b3887b54735b9663fd31a35db21
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Taniya Das <tdas@codeaurora.org>