Use BCMDHD SDIO for Orange Pi 5 Pro AP6256 Wi-Fi

## Summary - install `bcmdhd-sdio-dkms` for the Orange Pi 5 Pro AP6256 Wi-Fi module - blacklist the `brcmfmac` / `brcmutil` path for this board and set the BCMDHD firmware / NVRAM / config paths explicitly - replace the reboot-only `brcmfmac` unbind helper with a shutdown/reboot poweroff helper that cleanly powers down the SDIO Wi-Fi device ## Why On a real Orange Pi 5 Pro (AP6256 / BCM43456) running Ubuntu 24.04.1 with `6.1.0-1025-rockchip`, the default `brcmfmac` path was unstable: - sometimes `brcmf_attach` failed during boot - sometimes 5 GHz came up briefly and then disappeared after boot - the regression consistently reproduced on the same board / AP / image family Switching the board to the BCMDHD SDIO path fixed the issue in repeated live tests. ## Validation on hardware Validated on an Orange Pi 5 Pro connected to an 80 MHz / channel 36 5 GHz AP: - connected successfully to `CMCC-201-5G` on `5180 MHz` - remained connected past the previous failure window after cold boot - remained connected past the previous failure window after warm reboot - `bcmdhd_sdio` + `dhd_static_buf_sdio` were loaded instead of `brcmfmac` One representative boot sequence from the fixed system: - `wl_android_wifi_on : Success` - `Link UP with 48:81:d4:89:db:3f` - stable 5 GHz connection beyond 120 seconds (where the old path had already failed) If you want, I can also open a follow-up issue with the full before/after logs and exact local reproduction details. Fixes #1344 Related to #841