sched: Remove hack to enable/disable HMP scheduling extensions

The current method of turning HMP scheduling extensions on or off
based on the number of CPUs is inappropriate as there may be SoCs with
4 or less cores that require the use of these extensions. Remove this
hack as HMP extensions will now be enabled/disabled via command line
options.

Change-Id: Id44b53c2c3b3c3b83e1911a834e2c824f3958135
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>