drivers/am335xgpio: Migrate to adapter gpio commands

Use the new "adapter gpio" commands to configure the GPIOs used by the
am335xgpio driver. The AM335x has 4 GPIO 'chips' (chip number 0-3
inclusive), with each one providing 32 GPIOs (gpio_num 0-31 inclusive).

Change-Id: I7c63c0e4763657ea51790c43fc40d32b7c3580bb
Signed-off-by: Steve Marple <stevemarple@googlemail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6984
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>