jtag/adapter: Add command 'adapter gpio'

jtag/adapter: Add command 'adapter gpio'

Most adapters define their own commands to obtain the GPIO number and
other GPIO configuration information such as chip number, output drive
type, active high/low.

Define a general command 'adapter gpio' as replacement for the
driver-specific ones.

Change-Id: I1ca9ca94f0c7df5713172e9f62ffb0ad64e9ee97
Signed-off-by: Steve Marple <stevemarple@googlemail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6967
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>