include/linux/generic-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.

[akpm@linux-foundation.org: include math.h for round_up()]

Link: https://lkml.kernel.org/r/20211027150548.80042-1-andriy.shevchenko@linux.intel.comSigned-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/generic-radix-tree.h

@@ -38,8 +38,9 @@
 
 #include <asm/page.h>
 #include <linux/bug.h>
-#include <linux/kernel.h>
 #include <linux/log2.h>
+#include <linux/math.h>
+#include <linux/types.h>
 
 struct genradix_root;