power: Fix the PowerHAL on msm8974

 * Remove the CORE_CONTROL ifdefs, we need this code on 8974ac to
   signal mpctl about keeping extra cores online.
 * Remove an invalid hint- 8974 is not HMP and does not support
   the HMP boost hint.

Change-Id: I54036212bc240eede88a433d7cef661313fc8e5e