sched/tune: Increase the cgroup limit to 6

The schedtune cgroup controller allows upto 5 cgroups including the
default/root cgroup. Until now the user space is creating only
4 additional cgroups namely, foreground, background, top-app and
audio-app. Recently another cgroup called rt is created before
the audio-app cgroup. Since kernel limits the cgroups to 5, the
creation of audio-app cgroup is failing. Fix this by increasing
the schedtune cgroup controller cgroup limit to 6.

Change-Id: I13252a90dba9b8010324eda29b8901cb0b20bc21
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>