Add stm32f429i to the default build target

About time.

Change-Id: Iab389228bce18c0fc17d5ba4b24fe4ca4b0ad790
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/18356
Reviewed-by: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
Commit-Queue: Armando Montanez <amontanez@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 381f3cc..0a874f9 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -42,6 +42,7 @@
   deps = [
     ":docs",
     ":host",
+    ":stm32f429i",
   ]
 }