backport: jtag/drivers: add T-Head CK-Link JTAG adapter driver

[will-tm]

Driver for T-Head CK-Link Lite V2 probes, including the Bouffalo Lab BL616/BL702 CK-Link clones used as built-in debuggers on BL61x/BL70x evaluation boards. The wire protocol is a framed command format over USB bulk endpoints, reverse-engineered from T-Head's DebugServer.

Implements JTAG_SCAN via the probe's batch opcode, with IR caching across execute_queue boundaries and end-of-queue flush so OpenOCD's Capture-IR validation reads real hardware data. Speed is programmable (freq_kHz = 48000 / (N+1), capped at the DebugServer-validated 2526 kHz). Probes are matched against a built-in VID/PID list and by adapter serial.

Known protocol limitations, surfaced as one-time warnings:

• Single batch entry encodes IR/DR bit-counts in single bytes; scans > 255 bits are clamped with TDI pass-through on the un-shifted portion.
• The T-Head DTM's Capture-IR returns the current IR value rather than the IEEE 1149.1 'xxx01' pattern; init pre-loads IR = IDCODE.
• No TMS-sequence opcode: JTAG_TMS and JTAG_PATHMOVE return ERROR_JTAG_NOT_IMPLEMENTED.
• Multi-TAP chains are not supported.
• RTCK is not supported.

Tested against BL618 and BL702 evaluation boards.

Adapted for the Zephyr OpenOCD fork: uses .transports string array instead of .transport_ids, and the 4-argument jtag_libusb_open() signature (serial matching handled internally by libusb_helper).

Backport of:
https://review.openocd.org/c/openocd/+/9586