roll: third_party/pigweed: pw_channel: Add Rp2StdioChannel

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/217954
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https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: dc6f26bcbd2bda3..edf7501f5d03e8f
Roller-URL: https://ci.chromium.org/b/8744014520629755569
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CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ie2d3c438083c7a5107887bd9ae6b6de123a47f5a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/218612
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Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
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diff --git a/third_party/pigweed b/third_party/pigweed
index dc6f26b..edf7501 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit dc6f26bcbd2bda378b50d05f79370b58349bb811
+Subproject commit edf7501f5d03e8fb877e92f76defc63784d0171e