Fix epic_sleep() calls delaying load of new app

When core 1 repeatedly calls epic_sleep(), this could delay an epic_load() from core 0 because the reset interrupt can only be delivered after such a call completed.

To work around this, add calls into do_load() to notify the dispatcher task that it should return early from calls like epic_sleep(). This gets a bit tricky because the dispatcher task also uses ulTaskNotifyTake() to wake up when new API calls arrive. To make sure we still break out of epic_sleep(), we need to call xTaskNotifyGive() twice in the wait loop.