devfreq: Vote for bus bandwidth needed for the BWMON clocks

Some BWMON devices require clocks to be enabled. Some of these
clocks are dependent on the bus to be active before we enable
the clocks. Add code to vote for the bus bandwidth before enabling
the BWMON clocks.

Change-Id: Ic31f4f45ed59ba3fb5bcad007132fab30b1bd0b5
Signed-off-by: Rama Aparna Mallavarapu <aparnam@codeaurora.org>