vfs: take /proc/*/mounts and friends to fs/proc_namespace.c

rationale: that stuff is far tighter bound to fs/namespace.c than to
the guts of procfs proper.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/Makefile b/fs/Makefile
index d2c3353..310cfc4 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -19,6 +19,8 @@
 obj-y +=	no-block.o
 endif
 
+obj-$(CONFIG_PROC_FS) += proc_namespace.o
+
 obj-$(CONFIG_BLK_DEV_INTEGRITY) += bio-integrity.o
 obj-y				+= notify/
 obj-$(CONFIG_EPOLL)		+= eventpoll.o