msm: kgsl: Use CPU path to program pagetable when active count is 0

When active count is 0 then we should use the CPU path to program
pagetables because the GPU path requires event registration. Events
can only be queued when active count is valid. Hence, if the active
count is NULL then use the CPU path.

Change-Id: I70f5894d20796bdc0f592db7dc2731195c0f7a82
CRs-fixed: 481887
Signed-off-by: Shubhrapralash Das <sadas@codeaurora.org>