snippets: Added teensy bootloader snippet

Added a snippet that includes all Kconfig options and a dt overlay to
allow for easy use of the teensy bootloader.

Signed-off-by: Jan Behrens <[email protected]>

Author: jbehrensnx

snippets/pjrc-teensy-bootloader/README.rst

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+.. _snippet-pjrc-teensy-bootloader:
+
+PJRC Teensy Bootloader (pjrc-teensy-bootloader)
+#########################################
+
+.. code-block:: console
+
+   west build -S pjrc-teensy-bootloader [...]
+
+Overview
+********
+
+This snippet makes the nessecary configurations to allow flashing of Teensy 4
+based boards without triggering the reset pin. This is done via a CDC ACM UART.
+
+Requirements
+************
+
+A board that supports flashing via the teensy cli tools.
+
+A devicetree node with node label ``zephyr_udc0`` that points to an enabled USB
+device node with driver support. This should look roughly like this in
+:ref:`your devicetree <get-devicetree-outputs>`:
+
+.. code-block:: DTS
+
+   usb1: zephyr_udc0: usbd@402e0000 {
+      compatible = "nxp,ehci";
+        /* ... */
+   };
+
+The Teensy 4.0 and 4.1 boards have this node by default, but others might not.

snippets/pjrc-teensy-bootloader/pjrc-teensy-bootloader.conf

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+CONFIG_BOOTLOADER_TEENSY=y
+CONFIG_USB_DEVICE_VID=0x16c0
+CONFIG_USB_DEVICE_PID=0x0483
+
+CONFIG_USB_DEVICE_STACK=y
+CONFIG_USB_CDC_ACM=y
+CONFIG_CDC_ACM_DTE_RATE_CALLBACK_SUPPORT=y
+CONFIG_USB_DEVICE_INITIALIZE_AT_BOOT=y
+CONFIG_BOARD_LATE_INIT_HOOK=y

snippets/pjrc-teensy-bootloader/pjrc-teensy-bootloader.overlay

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+/*
+ * Copyright (c) 2025 Navimatix GmbH
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&zephyr_udc0 {
+	snippet_pjrc_teensy_bootloader_uart {
+		compatible = "zephyr,cdc-acm-uart";
+		label = "USB CDC-ACM";
+	};
+};

snippets/pjrc-teensy-bootloader/snippet.yml

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+name: pjrc-teensy-bootloader
+append:
+  EXTRA_CONF_FILE: pjrc-teensy-bootloader.conf
+  EXTRA_DTC_OVERLAY_FILE: pjrc-teensy-bootloader.overlay