sched: improve trace prints

Add the target and backup cpu in find_best_target trace print.
During placement print more information about the cpu before
skipping it. This helps in understanding why the cpu was not
considered for placement.

Change-Id: Ifc4de6b1d7495d2d701a92f465f4c81e86f468ea
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>