[roll third_party/pigweed] pw_spi_rp2040: Initiator implementation

Original-Bug: b/303255049
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/192791

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: d994a31af28c435..72840bdfdc5b67d
Roller-URL: https://ci.chromium.org/b/8755892279834376017
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I62887ce9a50c126c12627d1d3f0812f63135b25b
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/192883
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index d994a31..72840bd 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit d994a31af28c435e881b0dd070b6b38e2b329f59
+Subproject commit 72840bdfdc5b67d2cfcc05c5dc1c4f22fd7860a2