ring-buffer: export symbols

I'm adding a module to do a series of tests on the ring buffer as well
as benchmarks. This module needs to have more of the ring buffer API
exported. There's nothing wrong with reading the ring buffer from a
module.

[ Impact: allow modules to read pages from the ring buffer ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ring_buffer.c

@@ -2802,6 +2802,7 @@ void *ring_buffer_alloc_read_page(struct ring_buffer *buffer)
 
 	return bpage;
 }
+EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
 
 /**
  * ring_buffer_free_read_page - free an allocated read page
@@ -2814,6 +2815,7 @@ void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
 {
 	free_page((unsigned long)data);
 }
+EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
 
 /**
  * ring_buffer_read_page - extract a page from the ring buffer
@@ -2959,6 +2961,7 @@ int ring_buffer_read_page(struct ring_buffer *buffer,
  out:
 	return ret;
 }
+EXPORT_SYMBOL_GPL(ring_buffer_read_page);
 
 static ssize_t
 rb_simple_read(struct file *filp, char __user *ubuf,