timekeeping: Kill percpu.h dependency

Slimming down recursive header includes.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Thomas Gleixner <tglx@linutronix.de>

include/linux/hrtimer.h

@@ -16,7 +16,7 @@
 #include <linux/rbtree.h>
 #include <linux/init.h>
 #include <linux/list.h>
-#include <linux/percpu.h>
+#include <linux/percpu-defs.h>
 #include <linux/seqlock.h>
 #include <linux/timer.h>
 #include <linux/timerqueue.h>

include/linux/time_namespace.h

@@ -12,6 +12,8 @@
 struct user_namespace;
 extern struct user_namespace init_user_ns;
 
+struct vm_area_struct;
+
 struct timens_offsets {
 	struct timespec64 monotonic;
 	struct timespec64 boottime;