msm: kgsl: Add support for gpu busy multiplier

Adding support to increase/decrease gpu performance based on mod_percent.
This can be configured by user using new sysfs entry added in devfreq.
User needs to set mod_percent as multiplier percent which is used to
update measured GPU busy value before dcvs algorithm is run.
Example -
mod_percent = 120 (update gpu_busy to 120%)
mod_percent = 80 (update gpu_busy to 80%).

Change-Id: Ic6310b3a7751d5ccadd23332df76ddbcab450493
Signed-off-by: Pankaj Gupta <gpankaj@codeaurora.org>