fs: fix include/percpu-rwsem.h export error

We get the following export error on the include file:

usr/include/linux/fs.h:13: included file 'linux/percpu-rwsem.h' is not exported

Move the include inside the __KERNEL__ section.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/fs.h

@@ -10,7 +10,6 @@
 #include <linux/ioctl.h>
 #include <linux/blk_types.h>
 #include <linux/types.h>
-#include <linux/percpu-rwsem.h>
 
 /*
  * It's silly to have NR_OPEN bigger than NR_FILE, but you can change
@@ -417,6 +416,7 @@ struct inodes_stat_t {
 #include <linux/migrate_mode.h>
 #include <linux/uidgid.h>
 #include <linux/lockdep.h>
+#include <linux/percpu-rwsem.h>
 
 #include <asm/byteorder.h>