rcu: Don't include <linux/ktime.h> in rcutiny.h

The kbuild reported a built failure due to a header loop when RCUTINY is
enabled with my pending riscv-nommu port.  Switch rcutiny.h to only
include the minimal required header to get HZ instead.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

include/linux/rcutiny.h

@@ -12,7 +12,7 @@
 #ifndef __LINUX_TINY_H
 #define __LINUX_TINY_H
 
-#include <linux/ktime.h>
+#include <asm/param.h> /* for HZ */
 
 /* Never flag non-existent other CPUs! */
 static inline bool rcu_eqs_special_set(int cpu) { return false; }