roll: third_party/pigweed: pw_stream_uart_linux: Add Config struct

The config struct only has two basic properties for configuring the
UART - the baudrate, and a new property added by this change for
enabling flow control.

We opt to make the properties to the Config struct as std::optional to
allow the user to "keep" the default behaviour / previously set tty
behaviour. This maintains backwards compatability of this API and also
more closely resembles the Linux tty interface.

Original-Bug: 331871421
Test: CRTSCTS bit is processed on device serial uart driver on Open
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/233591

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 2fbf9d847123b2e..114064192788e79
Roller-URL: https://ci.chromium.org/b/8737699545199217153
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I2e0de384c55aaa495e27331de4125371cd92cf1a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/233957
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 2fbf9d8..1140641 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 2fbf9d847123b2ed2dfa2e9ff61cec2ba30324fc
+Subproject commit 114064192788e798a874673639f712441b803af4