sched/tune: Increase the cgroup limit to 7

We have 6 groups that is: background/ camera-daemon/ foreground/ rt/
top-app and root group. Adding another one for testing.

Bug: 144809570
Test: Build
Change-Id: I2d749a7bde4ad4c7c05f7218c9a5f39f8533acae
Signed-off-by: Wei Wang <wvw@google.com>