PM / devfreq: governor_bw_hwmon: Add suspend/resume support

Some devfreq devices using this governor might need suspend/resume support.
When suspended, those devices won't need any bandwidth votes and there is
no point in monitoring their bandwidth either.

Therefore, upon suspend, vote for zero bandwidth and stop the HW monitor.
Upon resume, vote for the previous bandwidth and start the HW monitor.

Change-Id: I318449995d714959f0ebfe91961bc23fa8edbd04
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
Signed-off-by: Rama Aparna Mallavarapu <aparnam@codeaurora.org>