sched: fair: Ignore energy-diff calculations for colocated tasks

Colocation is a performance-centric feature that drives tasks
to their preferred clusters in the wakeup cpu selection logic.
Let's not bother with energy-diff for these tasks even if the
previous CPU was not in the preferred cluster. This avoids
the overhead of the energy-diff calculation as well as the
potential failure to select a CPU in the preferred cluster.

Change-Id: I485905449175953b234f1efdb6817aab31b6de1e
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>