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/y2020/vision/sift/fast_gaussian.bzl b/y2020/vision/sift/fast_gaussian.bzl
index 5eaa4bf..b699282 100644
--- a/y2020/vision/sift/fast_gaussian.bzl
+++ b/y2020/vision/sift/fast_gaussian.bzl
@@ -39,6 +39,7 @@
             "roborio": "roborio",
             "armhf": "armhf-debian",
             "cortex-m": "cortex-m",
+            "cortex-m0plus": "cortex-m0plus",
         }),
         outs = headers + objects + htmls,
         # The tool doesn't support anything other than k8 and armhf-debian