restart_block: Trim includes

We don't actually use any timekeeping types, no need to pull in
time64.h.

Also, sched.h uses restart_block; add it as a direct dependency.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

include/linux/restart_block.h

@@ -7,8 +7,8 @@
 
 #include <linux/compiler.h>
 #include <linux/types.h>
-#include <linux/time64.h>
 
+struct __kernel_timespec;
 struct timespec;
 struct old_timespec32;
 struct pollfd;

include/linux/sched.h

@@ -34,6 +34,7 @@
 #include <linux/mm_types_task.h>
 #include <linux/task_io_accounting.h>
 #include <linux/posix-timers_types.h>
+#include <linux/restart_block.h>
 #include <linux/rseq.h>
 #include <linux/seqlock_types.h>
 #include <linux/kcsan.h>