msm: vidc: Refactor bandwidth management

Clean up the code base by renaming variables and using ktime_t instead
of fooling around with int64s when dealing with time.

Change-Id: Ibce54f251a416b022263a546ef79ca8268e76e6a
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>