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/tools/BUILD b/tools/BUILD
index 3acd443..2e470fa 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -34,6 +34,11 @@
     constraint_values = ["@//tools/platforms/hardware:cortex_m4f"],
 )
 
+config_setting(
+    name = "cpu_cortex_m0plus",
+    constraint_values = ["@//tools/platforms/hardware:cortex_m0plus"],
+)
+
 # TODO(phil): Re-enable this with proper support.
 #config_setting(
 #    name = "cpu_cortex_m4f_k22",