sched: walt: Update the wakeup timestamp for a non-new task

note_task_waking is defined under CONFIG_SCHED_HMP and thus
we will never update it with !CONFIG_SCHED_HMP selected.
This causes certain features to report max-load to the
governor resulting in unnecessary max-freq jumps. Add the
definition under CONFIG_SCHED_WALT. For now let's just
keep the wakeup-timestamp updation and leave the sleep
timestamp out of it.

Change-Id: I64ca38a9bfa1a61d042710e9ae7df208ca8a3a90
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>