m8: Keep two cores online

 * The recommended behavior for 8974pro is to keep two cores online
   at all times, as all cores can enter full power collapse at any
   time. Recently, we upgraded the perf lib which controlled this,
   and this new property is required to achieve the behavior we want.

Change-Id: I53d2197ca9aea80b10684ab436c9cc5b1c7f6c18