PM / devfreq: bw_hwmon: Move IRQ handling to device specific drivers

The bandwidth monitoring devices might have more than one IRQ to handle or
might have notifications from other drivers instead of using actual IRQs.
So, refactor the governor to move the IRQ handling to the bandwidth
monitoring device specific drivers and just provide an API that can be used
to request a re-evaluation.

The device specific driver can call this API to request an immediate
re-evaluation whenever the bandwidth has exceeded the previously set limit
instead of waiting for the periodic update.

Change-Id: I8bfd85d0cb59a1fd0116000aac430680e483b422
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>