sched: Compute avg_nr_running

Change-Id: I8ef699df0133d97c067ba225e633776f5006d32c
ghost: Kill most debugging by now

Signed-off-by: Zhao Wei Liew <zhaoweiliew@gmail.com>
Makefile: Add another graphite flag

Honestly, I don't know whether -fgraphite is an actual flag. Just put both flags in case.

Signed-off-by: Zhao Wei Liew <zhaoweiliew@gmail.com>