Revert "cpu: Fix generic idle thread allocation"

This reverts commit a9a01442dd1079dccfa1bfc55154055f5c643ce9.
Revert "arm: Use generic idle thread allocation"

This reverts commit 8044b84bfde7070028a75d0e938ad63a4a71d509.
Revert "smp: Add task_struct argument to __cpu_up()"

This reverts commit ed5fd375c5f5384b933b7ee93c4f70adf9b07232.