msm: kgsl: Account for throttled clock cycles in DCVS

Limits management can force clock throttling which results in incorrect
busy percentage calculation. We need to account for that in DCVS.

Change-Id: Iaa17a7f7d661ab9966597f7710374d5b2e00d514
Signed-off-by: Oleg Perelet <operelet@codeaurora.org>