sched: Refactor HMP code to allow easier rebasing

Move the HMP implementation to the end of each of
the scheduler files in order to allow incoming
merges to not conflict with upstream code.
All HMP declarations are placed at the top of each
file.

Change-Id: Ibf8e066840137cf84f32aa97a5aadb709f949261
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>