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/WORKSPACE b/WORKSPACE
index d532887..8a49b63 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -123,6 +123,7 @@
     "//tools/cpp:cc-toolchain-armhf-debian",
     "//tools/cpp:cc-toolchain-roborio",
     "//tools/cpp:cc-toolchain-cortex-m4f",
+    "//tools/cpp:cc-toolchain-rp2040",
     # Find a good way to select between these two M4F toolchains.
     #"//tools/cpp:cc-toolchain-cortex-m4f-k22",
     "//tools/python:python_toolchain",