sched/walt: Fix the memory leak of idle task load pointers

The memory for task load pointers are allocated twice for each
idle thread except for the boot CPU. This happens during boot
from idle_threads_init()->idle_init() in the following 2 paths.

1. idle_init()->fork_idle()->copy_process()->
		sched_fork()->init_new_task_load()

2. idle_init()->fork_idle()-> init_idle()->init_new_task_load()

The memory allocation for all tasks happens through the 1st path,
so use the same for idle tasks and kill the 2nd path. Since
the idle thread of boot CPU does not go through fork_idle(),
allocate the memory for it separately.

Change-Id: I4696a414ffe07d4114b56d326463026019e278f1
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>