ANDROID: sched: Add vendor hook for update_load_sum

vendor may have the need to modify update_load_sum function

Bug: 344826816
Bug: 181105055
Change-Id: I35964977a4b8917c62773d48a37340f880774e38
Signed-off-by: Chungkai Mei <chungkai@google.com>
(cherry picked from commit 984523c3)
(cherry picked from commit 0d97bca8)
[Trivial conflict in include/trace/hooks/sched.h and vendor_hooks.c due
to new code added and code ordering]
Signed-off-by: Qais Yousef <qyousef@google.com>