roll: third_party/pigweed pw_uart_mcuxpresso: Simplify configuration struct

- Utilize the pw_dma_mcuxpresso module to manage DMA channels.
- Directly query flexcomm clock freq after the clock is turned on during
  init.

Also fix const application in pw_dma_mcuxpresso that arm compiler in mac
CI didn't like and looked like a mistake anyways. This was needed to
dma_uart_example.cc could compile.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/236919
Original-Revision: ca679a238320e25cdf6649e74dcb76af21e2beb9

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: a4dab0be18a649..ca679a238320e2
Roller-URL: https://ci.chromium.org/b/8735874310189115841
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Iaebb32fd2bc247e2f633ff2e53d1e9ac61d1072e
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/237735
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index a4dab0b..ca679a2 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit a4dab0be18a649c79759880308ed051b0a2576a4
+Subproject commit ca679a238320e25cdf6649e74dcb76af21e2beb9