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/hex.bzl b/third_party/pico-sdk/hex.bzl
new file mode 100644
index 0000000..5e9dfae
--- /dev/null
+++ b/third_party/pico-sdk/hex.bzl
@@ -0,0 +1,25 @@
+def bin_from_elf(name, target_compatible_with = None):
+    native.genrule(
+        name = name,
+        srcs = ["%s.elf" % name],
+        outs = ["%s.bin" % name],
+        cmd = "$(OBJCOPY) -Obinary $< $@",
+        executable = True,
+        output_to_bindir = True,
+        target_compatible_with = target_compatible_with,
+        toolchains = ["@bazel_tools//tools/cpp:current_cc_toolchain"],
+    )
+
+def uf2_from_elf(name, target_compatible_with = None):
+    native.genrule(
+        name = name,
+        srcs = ["%s.elf" % name],
+        outs = ["%s.uf2" % name],
+        cmd = "$(location //third_party/pico-sdk/tools/elf2uf2) $< $@",
+        executable = True,
+        output_to_bindir = True,
+        target_compatible_with = target_compatible_with,
+        tools = [
+            "//third_party/pico-sdk/tools/elf2uf2",
+        ],
+    )