kernfs: Replace kernel.h with the necessary inclusions

When kernel.h is used in the headers it adds a lot into dependency hell,
especially when there are circular dependencies are involved.

Replace kernel.h inclusion with the list of what is really being used.
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211209123008.3391-1-andriy.shevchenko@linux.intel.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/kernfs.h

@@ -6,7 +6,6 @@
 #ifndef __LINUX_KERNFS_H
 #define __LINUX_KERNFS_H
 
-#include <linux/kernel.h>
 #include <linux/err.h>
 #include <linux/list.h>
 #include <linux/mutex.h>
@@ -14,6 +13,8 @@
 #include <linux/lockdep.h>
 #include <linux/rbtree.h>
 #include <linux/atomic.h>
+#include <linux/bug.h>
+#include <linux/types.h>
 #include <linux/uidgid.h>
 #include <linux/wait.h>
 #include <linux/rwsem.h>
@@ -23,6 +24,7 @@ struct dentry;
 struct iattr;
 struct seq_file;
 struct vm_area_struct;
+struct vm_operations_struct;
 struct super_block;
 struct file_system_type;
 struct poll_table_struct;