Add interrupt support for emulator

This provides us a way to inject interrupts during a test. If a test has
interrupt_generator() defined, it will run in a separate thread. The
generator can then trigger interrupts when it decides to. The current
running task is suspended while emulator is executing ISR.

Also fixes a bug that tasks run without scheduler notifying them during
emulator start-up.

BUG=chrome-os-partner:19235
TEST=Repeatedly run all tests.
BRANCH=None

Change-Id: I0f921c47c0f848a9626da6272d9040e2b7c5ac86
Signed-off-by: Vic Yang <victoryang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/55671

test/interrupt.tasklist

@@ -0,0 +1,17 @@
+/* Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/**
+ * List of enabled tasks in the priority order
+ *
+ * The first one has the lowest priority.
+ *
+ * For each task, use the macro TASK_TEST(n, r, d, s) where :
+ * 'n' in the name of the task
+ * 'r' in the main routine of the task
+ * 'd' in an opaque parameter passed to the routine at startup
+ * 's' is the stack size in bytes; must be a multiple of 8
+ */
+#define CONFIG_TEST_TASK_LIST  /* No test task */