Very interesting!
https://patchwork.ozlabs.org/patch/927445/
brcm2708: Add support for CYW43455
is not approved.
But these are!
linux-firmware: add firmware for BCM43455 SDIO wlan...
brcm2708: add RPi3+ wifi calibration data
brcm2708: add brcmfmac-firmware-43455-sdio to DEFAULT_PACKAGES
brcm2708: move wifi calibration EEPROMs out of base...
I'm very sorry to say so but this brcmfmac43455-sdio.bin from
linux-firmware.git commited 2015-03-20 does not work for me!