sysfs, kernfs: move file core code to fs/kernfs/file.c

Move core file code to fs/kernfs/file.c.  fs/sysfs/file.c now contains
sysfs kernfs_ops callbacks, sysfs wrappers around kernfs interfaces,
and sysfs_schedule_callback().  The respective declarations in
fs/sysfs/sysfs.h are moved to fs/kernfs/kernfs-internal.h.

This is pure relocation.

v2: Refreshed on top of the v2 of "sysfs, kernfs: prepare read path
    for kernfs".

v3: Refreshed on top of the v3 of "sysfs, kernfs: prepare read path
    for kernfs".

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 31f0dbe..38e3a16 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -142,4 +142,11 @@
 void sysfs_addrm_finish(struct sysfs_addrm_cxt *acxt);
 struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type);
 
+/*
+ * file.c
+ */
+extern const struct file_operations kernfs_file_operations;
+
+void sysfs_unmap_bin_file(struct sysfs_dirent *sd);
+
 #endif	/* __KERNFS_INTERNAL_H */