Add basic rpi2040 blink demo app

Phew, things build!  Lets check in how far we got.

Change-Id: Id82e2f4c73eed6620b2b4661726f931e79a6b0c1
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/frc971/imu/blink.c b/frc971/imu/blink.c
new file mode 100644
index 0000000..d478d78
--- /dev/null
+++ b/frc971/imu/blink.c
@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include "pico/stdlib.h"
+
+int main() {
+#ifndef PICO_DEFAULT_LED_PIN
+#warning blink example requires a board with a regular LED
+#else
+    const uint LED_PIN = PICO_DEFAULT_LED_PIN;
+    gpio_init(LED_PIN);
+    gpio_set_dir(LED_PIN, GPIO_OUT);
+    while (true) {
+        gpio_put(LED_PIN, 1);
+        sleep_ms(250);
+        gpio_put(LED_PIN, 0);
+        sleep_ms(250);
+    }
+#endif
+}