drivers/am335xgpio: Add AM335x driver for bitbang support on BeagleBones

Change-Id: Iac1c9f3d380e2474c8b77407c89c2aad96fbf2ea
Signed-off-by: Steve Marple <stevemarple@googlemail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6941
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

tcl/interface/beaglebone-swd-native.cfg

@@ -0,0 +1,29 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# BeagleBone native GPIO interface for SWD
+#
+# This is best used with a fast buffer but it is also suitable for a direct
+# connection if the target voltage matches the host's IO voltage (typically
+# 3.3V) and the cable is short.
+#
+# DO NOT APPLY VOLTAGE TO THE GPIO PINS UNTIL SYS_RESETN IS HIGH.
+#
+# Do not forget the GND connection.
+
+adapter driver am335xgpio
+
+# Transition delay calculation: SPEED_COEFF/khz - SPEED_OFFSET
+# These depend on the system clock, calibrated for stock 1 GHz BeagleBoneBlack
+# am335xgpio speed SPEED_COEFF SPEED_OFFSET
+am335xgpio speed_coeffs 600000 575
+
+am335xgpio swclk_num 2
+am335xgpio swdio_num 4
+am335xgpio swdio_dir_num 60
+am335xgpio swdio_dir_output_state on
+
+# USR0 LED
+am335xgpio led_num 53
+am335xgpio led_on_state on
+
+am335xgpio srst_num 65
+reset_config srst_only srst_push_pull