sched: uninline scheduler

* save ~300 bytes
* activate_idle_task() was moved to avoid a warning

bloat-o-meter output:

add/remove: 6/0 grow/shrink: 0/16 up/down: 438/-733 (-295)		<===
function                                     old     new   delta
__enqueue_entity                               -     165    +165
finish_task_switch                             -     110    +110
update_curr_rt                                 -      79     +79
__load_balance_iterator                        -      32     +32
__task_rq_unlock                               -      28     +28
find_process_by_pid                            -      24     +24
do_sched_setscheduler                        133     123     -10
sys_sched_rr_get_interval                    176     165     -11
sys_sched_getparam                           156     145     -11
normalize_rt_tasks                           482     470     -12
sched_getaffinity                            112      99     -13
sys_sched_getscheduler                        86      72     -14
sched_setaffinity                            226     212     -14
sched_setscheduler                           666     642     -24
load_balance_start_fair                       33       9     -24
load_balance_next_fair                        33       9     -24
dequeue_task_rt                              133      67     -66
put_prev_task_rt                              97      28     -69
schedule_tail                                133      50     -83
schedule                                     682     594     -88
enqueue_entity                               499     366    -133
task_new_fair                                317     180    -137

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Signed-off-by: Ingo Molnar <mingo@elte.hu>