ftdi: replace proprietary libftd2xx with open-source libftdi1

The Olimex ARM-USB-OCD (and any FT2232 with a custom USB id) couldn't be
enumerated by libftd2xx and needed a manual ftdi_sio unbind. libftdi1
(libusb) opens any VID:PID and auto-detaches the kernel driver.

- rewrite drivers/ftdi_jtag on libftdi1: enumerate a known VID:PID list
  (incl. Olimex 15ba:0003/002b) with per-chip channel counts, open by
  bus/addr + interface, MPSSE via ftdi_write_data/ftdi_read_data (+
  SEND_IMMEDIATE for deterministic reads). MPSSE command building, pin
  map and clocking unchanged.
- CMake: link libftdi1 + libusb-1.0 (pkg-config), drop FTDILIB/FTD2XX
  defines and the libftd2xx.a link; remove the vendored src/libs/libftd2xx.
- registry: NXP LPC2103 (ARM7TDMI-S) entry, IDCODE 0x4F1F0F0F.
- docs updated (deps, layout, decision note, roadmap phase 8).

Validated on hardware: ARM-USB-OCD enumerates, jtag_scan reads the
LPC2103 IDCODE 0x4F1F0F0F, target_info -> [cpu, ARM7] prog: arm_flash.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

doc/tutorial.md

@@ -15,8 +15,8 @@ only the IDCODE and BSDL filename change.
 ## Prerequisites
 
 - A JTAG probe physically wired to the target's TCK/TDI/TDO/TMS/TRST.
-- `libftd2xx` reachable at runtime (already vendored under
-  `src/libs/libftd2xx/`).
+- `libftdi1` + `libusb-1.0` installed (Arch: `libftdi`; Debian:
+  `libftdi1-dev`) — open source, drives FTDI/Olimex probes.
 - The target's BSDL in `data/bsdl_files/` (KU15P: `xcku15p_ffve1517.bsd` is
   bundled).
 - An entry for the target in `data/targets.yaml` (KU15P is bundled).