PM / devfreq: icc: add support for L3 voting

Add support for L3 voting in the devfreq icc driver.
This includes populating the device's OPP table with L3
frequencies from HW and voting in this same unit of Hz
as accepted by the L3 interconnect provider.

Change-Id: I877f41324b55b333f4e5ef9f34232563357712c8
Signed-off-by: Amir Vajid <avajid@codeaurora.org>