freezer: don't unnecessarily set PF_NOFREEZE explicitly

Some drivers set PF_NOFREEZE in their kthread functions which is
completely unnecessary and racy - some part of freezer code doesn't
consider cases where PF_NOFREEZE is set asynchronous to freezer
operations.

In general, there's no reason to allow setting PF_NOFREEZE explicitly.
Remove them and change the documentation to note that setting
PF_NOFREEZE directly isn't allowed.

-v2: Dropped change to twl4030-irq.c as it no longer uses PF_NOFREEZE.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: "Gustavo F. Padovan" <padovan@profusion.mobi>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Cc: Marcel Holtmann <marcel@holtmann.org>
Cc: wwang <wei_wang@realsil.com.cn>
diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt
index 316c2ba..587e082 100644
--- a/Documentation/power/freezing-of-tasks.txt
+++ b/Documentation/power/freezing-of-tasks.txt
@@ -67,7 +67,7 @@
 
 Kernel threads are not freezable by default.  However, a kernel thread may clear
 PF_NOFREEZE for itself by calling set_freezable() (the resetting of PF_NOFREEZE
-directly is strongly discouraged).  From this point it is regarded as freezable
+directly is not allowed).  From this point it is regarded as freezable
 and must call try_to_freeze() in a suitable place.
 
 IV. Why do we do that?