sched: Move core_ctl callback from tick to WALT IRQ work

The WALT window size and tick period can be different. Hence move
core_ctl callback from tick to WALT IRQ work. As all online CPUs's
windows are rolled over in this work, core_ctl can query the load
without worrying about window rollover.

Change-Id: I5e0bc8f3508f02f68690df67f322b89350ead25c
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>