hw/bsp/ch58x: address review feedback and read the real chip unique id

Fold in the CH58x BSP review fixes:

- family.mk: drop stray trailing backslashes on the last LDFLAGS/SRC_C entries
  (harmless -- GNU Make ends the list at the blank line -- but misleading).
- debug_uart.c: uart_write() spun on a full ring buffer with nothing to drain it
  (only uart_sync() advances tx_consume), so a burst larger than the buffer
  deadlocked. Drain the FIFO while waiting, like uart_sync() does.
- wch-riscv.cfg: move the OpenOCD work area from 0x80000000 (unmapped) to the
  0x20000000 SRAM, sized to 32 KB, matching ch32v20x/wch-riscv.cfg.
- family.c: implement board_get_unique_id() from the factory MAC. CH58x is a BLE
  part, so a unique 6-byte MAC lives in FlashROM at ROM_CFG_MAC_ADDR; GetMACAddress()
  reads it via FLASH_EEPROM_CMD (in libISP583.a), so no extra source file is needed.
  The read buffer is TU_ATTR_ALIGNED(4) and 8 bytes, per the SDK's documented
  4-byte-aligned, word-granular buffer contract (CH58x_flash.c).
- test/hil/tinyusb.json: key ch582m_evt off this board's actual MAC (D443627B5450)
  instead of the fixed placeholder, like every other board.

Verified on ci.lan HIL: ch582m_evt enumerates with serial D443627B5450 and all
device examples pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/hil/tinyusb.json

@@ -496,7 +496,7 @@
         },
         {
             "name": "ch582m_evt",
-            "uid": "0123456789ABCDEF",
+            "uid": "D443627B5450",
             "toolchain": "riscv-gcc",
             "tests": {
                 "device": true,