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/third_party/pico-sdk/tools/elf2uf2/BUILD b/third_party/pico-sdk/tools/elf2uf2/BUILD
new file mode 100644
index 0000000..98b8209
--- /dev/null
+++ b/third_party/pico-sdk/tools/elf2uf2/BUILD
@@ -0,0 +1,19 @@
+cc_binary(
+    name = "elf2uf2",
+    srcs = [
+        "elf.h",
+        "main.cpp",
+    ],
+    copts = [
+        "-Wno-format-nonliteral",
+        "-Wno-reorder",
+        "-Wno-unused-parameter",
+        "-Wno-unused-function",
+    ],
+    includes = ["."],
+    target_compatible_with = ["@platforms//os:linux"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//third_party/pico-sdk/src/common/boot_uf2",
+    ],
+)