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>

README.md

@@ -38,7 +38,10 @@ and Microsemi IGLOO2 M2GL010T (`m2gl010t-fg484.bsd`). Add more by dropping
 - `readline` (Arch: `readline`, Debian/Ubuntu: `libreadline-dev`)
 - `libyaml` for the FPGA registry, found via pkg-config `yaml-0.1`
   (Arch: `libyaml`, Debian/Ubuntu: `libyaml-dev`)
-- `libftd2xx` for FTDI probes (vendored in `src/libs/libftd2xx/`)
+- `libftdi1` + `libusb-1.0` for FTDI/Olimex probes, via pkg-config
+  `libftdi1` (Arch: `libftdi`, Debian/Ubuntu: `libftdi1-dev`). Open
+  source — no vendored proprietary SDK; works with any VID:PID and
+  auto-detaches the kernel `ftdi_sio` driver.
 - *To drive a Digilent SMT2/SMT2-NC probe:* the Digilent
   [Adept Runtime](https://digilent.com/shop/software/digilent-adept/)
   installed system-wide (provides `libdjtg.so` + `libdmgr.so`).
@@ -176,9 +179,8 @@ shows it).
 ## Repository layout
 
 ```
-src/                   — code + libs —
+src/
 ├── bs/                Application (readline REPL)
-├── libs/libftd2xx/    Vendored FTDI SDK
 └── modules/
     ├── jtag_core/     TAP state machine, IR/DR shifts
     ├── bsdl_parser/   .bsd loader