sched: Fix for 32bit '__udivdi3' build error

Undefined reference to '__udivdi3' error happened
when build for 32bit. Use div64_ul for both compatible
for arm64 and arm.

Change-Id: I20c0c4629b413238e0546479aad239eca0f49d35
Signed-off-by: Maria Yu <aiquny@codeaurora.org>