add jtag debug configs for openocd

dbg.sh

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+openocd -f interface/jlink.cfg -f board/rpi4b.cfg

jlink.cfg

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+# SPDX-License-Identifier: GPL-2.0-or-later
+
+#
+# SEGGER J-Link
+#
+# http://www.segger.com/jlink.html
+#
+
+adapter driver jlink
+
+# The serial number can be used to select a specific device in case more than
+# one is connected to the host.
+#
+# Example: Select J-Link with serial number 123456789
+#
+# adapter serial 123456789

rpi4b.cfg

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+# SPDX-License-Identifier: GPL-2.0-or-later
+
+# This is the Raspberry Pi 4 model B board with BCM2711 chip
+# https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2711/README.md
+#
+# Enable JTAG GPIO on Raspberry Pi boards
+# https://www.raspberrypi.org/documentation/configuration/config-txt/gpio.md
+
+source [find target/bcm2711.cfg]
+transport select jtag
+
+# Raspberry Pi boards only expose Test Reset (TRST) pin, no System Reset (SRST)
+reset_config trst_only