ANDROID: sched: add restrict vendor hook to modify load balance behavior

For modifying load balance policy, we add the hook on
find_busiest_group().
It allows us to modify load balance paths.

Bug: 168248326
Signed-off-by: YT Chang <yt.chang@mediatek.com>
Change-Id: I77ec043576139806551b978eb1bdf9f637442dfb
(cherry picked from commit a2ca8408de6183364b4c17f341f06e875bc7a1c1)
(cherry picked from commit 489646b879ede582b6b00803edd3f777aede4d85)