sched/fair: Pass arguments to find_best_target() in a structure

Refactor find_energy_efficient_cpu() to pass additional arguments
to find_best_target() via find_best_target_env structure. The
subsequent patches use this structure add more features like
need_idle to influence the CPU selection in find_best_target().

Change-Id: I2e2c3de237bf78a364ea6c68285a8a96e5ae6c61
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>