headers: remove sched.h from interrupt.h

After m68k's task_thread_info() doesn't refer to current,
it's possible to remove sched.h from interrupt.h and not break m68k!
Many thanks to Heiko Carstens for allowing this.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>

arch/um/drivers/port_kern.c

@@ -7,6 +7,7 @@
 #include "linux/interrupt.h"
 #include "linux/list.h"
 #include "linux/mutex.h"
+#include "linux/workqueue.h"
 #include "asm/atomic.h"
 #include "init.h"
 #include "irq_kern.h"