[roll third_party/pigweed] targets/rp2040: Auto generate uf2 files

Adds build integration to build the elf2uf2 tool and then use it to
generate uf2 files alongside every ELF file.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/109810

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: cf4afce96fe9c62..7268723116f5d2e
Roller-URL: https://ci.chromium.org/b/8803189453561658561
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I59331be7683dc2c5d942c602406646b7e33aef44
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/110143
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index cf4afce..7268723 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit cf4afce96fe9c62ba37c1f81203bfc0f73b51614
+Subproject commit 7268723116f5d2e0d4b7a194315906b8af97e223