chipset/zephyr: add guide to turn nrf5340 development boards into HCI USB dongles

chipset/zephyr/nrf5340_dongle/README.md

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+# nRF5340 (Audio) DK Board as USB HCI Dongle Guide
+
+This will turn the Nordic nRF5340 DK and Audio DK boards into an USB CDC HCI dongle.
+
+If using the NRF Connect SDK ( sdk-nrf ) it is important to follow the order in this document, as 'west flash' 
+will also program the NetCore with zephyr-ll which needs to be replaced afterwards with the Packetcraft Link Layer.
+
+## Preconditions
+Copy the included files to '${ZEPHYR_ROOT}/zephyr/examples/bluetooth/hci_uart/'
+
+## Build/Flash HCI Bridge on AppCore
+
+You need to specify the board with the '-b' param in the west call.
+
+For nRF5340 DK:
+
+```sh
+cd  ${ZEPHYR_ROOT}/zephyr/samples/bluetooth/hci_uart/
+west build --pristine -b nrf5340dk_nrf5340_cpuapp -- -DDTC_OVERLAY_FILE=usb.overlay -DOVERLAY_CONFIG=overlay-usb.conf
+west flash
+```
+
+For nRF5340 Audio DK (ADK)
+
+```sh
+cd  ${ZEPHYR_ROOT}/zephyr/samples/bluetooth/hci_uart/
+west build --pristine -b nrf5340_audio_dk_nrf5340_cpuapp -- -DDTC_OVERLAY_FILE=usb.overlay -DOVERLAY_CONFIG=overlay-usb.conf
+west flash
+```
+
+## Flash Packetcraft Link Layer on NetCore
+
+```sh
+nrfjprog --program ble5-ctr-rpmsg_3424.hex --chiperase --coprocessor CP_NETWORK -r --verify
+```
+
+the corresponding hex file is in the [nrfConnectSDK](https://github.com/nrfconnect/sdk-nrf/blob/main/lib/bin/bt_ll_acs_nrf53/bin)
+
+## Usage / Find Serial Port
+
+On macOS, the nRF5340 with the HCI bridge show up as 5 /dev/tty. To find the HCI one, list all /dev/tty.* devices,
+then press and hold the RESET button and list all devices again. The missing one is the one provided by the HCI bridge.
+
+## HCI log
+
+```sh
+btmon -J nrf5340_xxaa_app -w <logfile>
+```

chipset/zephyr/nrf5340_dongle/overlay-usb.conf

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+#USB stuff
+CONFIG_USB_DEVICE_STACK=y
+CONFIG_USB_DEVICE_PRODUCT="Zephyr HCI UART sample"
+CONFIG_USB_CDC_ACM=y
+CONFIG_USB_DEVICE_INITIALIZE_AT_BOOT=n
+
+#CONFIG_USB_DEVICE_LOG_LEVEL_DBG=y
+
+# stack
+#CONFIG_ISR_STACK_SIZE=8192
+#CONFIG_IDLE_STACK_SIZE=8192
+#CONFIG_MAIN_STACK_SIZE=8192
+#CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=8192
+#CONFIG_IPC_SERVICE_BACKEND_RPMSG_WQ_STACK_SIZE=8192
+#CONFIG_HEAP_MEM_POOL_SIZE=8192
+
+# Enable ISO support
+CONFIG_BT_ISO_BROADCASTER=y
+CONFIG_BT_ISO_TX_BUF_COUNT=10
+CONFIG_BT_ISO_TX_MTU=251
+CONFIG_BT_ISO_RX_BUF_COUNT=10
+CONFIG_BT_ISO_RX_MTU=251
+
+# setup rpmsg/Bluetooth buffer
+CONFIG_BT_BUF_EVT_RX_COUNT=16
+CONFIG_BT_BUF_EVT_RX_SIZE=255
+CONFIG_BT_BUF_ACL_RX_SIZE=255
+CONFIG_BT_BUF_ACL_TX_SIZE=251
+CONFIG_BT_BUF_CMD_TX_SIZE=255
+
+#debug stuff
+#CONFIG_ASSERT=y
+
+#CONFIG_THREAD_NAME=y
+#CONFIG_THREAD_ANALYZER=y
+#CONFIG_THREAD_ANALYZER_AUTO=y
+#CONFIG_THREAD_ANALYZER_RUN_UNLOCKED=y
+
+#CONFIG_HW_STACK_PROTECTION=y
+
+#CONFIG_CONSOLE=n
+#CONFIG_LOG=y
+#CONFIG_LOG_BUFFER_SIZE=4096
+#CONFIG_RTT_CONSOLE=y
+#CONFIG_UART_CONSOLE=n
+#CONFIG_LOG_BACKEND_RTT=y
+#CONFIG_LOG_BACKEND_RTT_MODE_DROP=n
+#CONFIG_USE_SEGGER_RTT=y
+#CONFIG_SEGGER_RTT_BUFFER_SIZE_UP=2048
+#CONFIG_LOG_BACKEND_SHOW_COLOR=n
+#CONFIG_LOG_PROCESS_THREAD_STACK_SIZE=8192
+
+#CONFIG_LOG_DEFAULT_LEVEL=3

chipset/zephyr/nrf5340_dongle/usb.overlay

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+/*
+ * Copyright (c) 2021 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+ */
+
+/ {
+	chosen {
+		zephyr,bt-c2h-uart = &cdc_acm_uart0;
+	};
+};
+
+&zephyr_udc0 {
+	cdc_acm_uart0: cdc_acm_uart0 {
+		compatible = "zephyr,cdc-acm-uart";
+	};
+};