The stack of a task has been separated from the memory of a task_struct
struture for a long time on x86, as a result __{start,end}_init_task no
longer mark the start and end of the init_task structure, but its stack
only.
Rename __{start,end}_init_task to __{start,end}_init_stack.
Note other architectures are not affected because __{start,end}_init_task
are used on x86 only.
Signed-off-by: Xin Li (Intel) <xin@xxxxxxxxx>