include/linux/radix-tree.h: 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.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Andy Shevchenko <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/radix-tree.h

@@ -9,8 +9,10 @@
 #define _LINUX_RADIX_TREE_H
 
 #include <linux/bitops.h>
-#include <linux/kernel.h>
+#include <linux/gfp.h>
 #include <linux/list.h>
+#include <linux/lockdep.h>
+#include <linux/math.h>
 #include <linux/percpu.h>
 #include <linux/preempt.h>
 #include <linux/rcupdate.h>