adapter: Rework parallel port driver

Make the driver more flexible and define adapter-specific configurations
in Tcl instead of C using the adapter GPIO subsystem.

The rework also includes coding style fixes and improvements of the
documentation. All modifications are done such that backwards
compatibility is ensured.

Tested with Olimex ARM-JTAG cable [1] and APM32F103 target device on
Linux and FreeBSD. The driver works on Linux using direct I/O and PPDEV.
On FreeBSD, only PPDEV works. The build with direct I/O already failed
before the patch. This problem will be fixed in a subsequent patch.

The patch is not tested on Windows because there is no documentation
for it.

[1] https://www.olimex.com/Products/ARM/JTAG/ARM-JTAG/

Change-Id: Ib671d52a919eaf2959cf6365f2c8004257ae074c
Signed-off-by: Marc Schink <dev@zapb.de>
Reviewed-on: https://review.openocd.org/c/openocd/+/8943
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins

tcl/interface/parport/flashlink.cfg

@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+adapter driver parport
+
+adapter gpio tdo 12 -active-low -exit-inactive
+adapter gpio trst 6 -exit-inactive
+adapter gpio tms 3 -exit-inactive
+adapter gpio tck 2 -exit-inactive
+adapter gpio tdi 4 -exit-inactive
+adapter gpio srst 7 -exit-inactive
+
+transport select jtag