msm: kgsl: Align busy times with the end times of samples

Make sure that the busy times are calculated at the end of the
current sample and before the next sample starts. This prevents
false alarms of busy timer events being triggered. Applies only
to devices with idlestats power policy.

Change-Id: I1e28fff4128b72c25e8073d845d519867d67a9ca
Signed-off-by: Ranjhith Kalisamy <ranjhith@codeaurora.org>