[roll third_party/pigweed] pw_stream_uart_linux: Add stream for UART on Linux

This adds a pw::stream implementation that can be used to read/write
from UART devices on Linux.

Tested: Built with gn, bazel, and Android. Exercised functionality from
an Android service.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/156910

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: e89ac8201c40a93..3fb983d9e8f95cd
Roller-URL: https://ci.chromium.org/b/8774666655581816449
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Iff5d729e8e82f6af18bbaaa1c2c435bb10711a74
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/158750
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.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 e89ac82..3fb983d 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit e89ac8201c40a9360f15bcbf0a9ffd77c160d1e8
+Subproject commit 3fb983d9e8f95cdac801d9dac6426a15fe316d00