sched: Use capacity_orig_of instead of capacity_of in overutilized function

At present __cpu_overutilized() determines whether CPU is overutilized
or not by using capacity_of(). CPU's capacity can be reduced by RT tasks
load and using capacity_of() may lead to undesired behavior. So, use
capacity_orig_of() instead of capacity_of() to find CPU is overutilized
or not.

While at it, remove double accounting of cpu utilization for RT tasks.

Change-Id: I55b1a782f5b4ad859ee88cd43d5236b8187db2ea
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>