PM / devfreq: bw_hwmon: Expose a throttle adjust tunable

Newer versions of bimc-bwmon counters have the capability to fake
higher byte count than what's actually transferred between a bus
master and DDR if the bus master is being throttled by QoS hardware
logic. Add support to set the throttle adjust field that comes with
this newer version of bimc-bwmon.

Change-Id: I33376c825fb11ab2e378f828b1d2ae46dd582836
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>