percpu: remove some sparse warnings

Make the following changes to remove some sparse warnings.

* Make DEFINE_PER_CPU_SECTION() declare __pcpu_unique_* before
  defining it.

* Annotate pcpu_extend_area_map() that it is entered with pcpu_lock
  held, releases it and then reacquires it.

* Make percpu related macros use unique nested variable names.

* While at it, add pcpu prefix to __size_call[_return]() macros as
  to-be-implemented sparse annotations will add percpu specific stuff
  to these macros.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/mm/percpu.c b/mm/percpu.c
index ec158bb..e2e80fc 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -365,6 +365,7 @@
  * 0 if noop, 1 if successfully extended, -errno on failure.
  */
 static int pcpu_extend_area_map(struct pcpu_chunk *chunk)
+	__releases(lock) __acquires(lock)
 {
 	int new_alloc;
 	int *new;