irq: Add an irq_poll() stub for board code

Allow the board specific code to run checks prior to running each
task.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/sched.c

@@ -268,6 +268,7 @@ run_task(void)
 {
     struct callback_handler *p;
     foreachdecl(p, taskfuncs) {
+        irq_poll();
         void (*func)(void) = READP(p->func);
         func();
     }