sched: fair: Account PELT estimated utilization on WALT disabled cpu_util_cum

This improves scheduler decision accuracy, on load balancing and EAS placement
specifically

Change-Id: I21733de68d9796e2c69605102e0fb5ea60e742b5
Signed-off-by: Diep Quynh <remilia.1505@gmail.com>
Signed-off-by: Alexander Winkowski <dereference23@outlook.com>