brcmfmac: firmware: Allow per-board firmware binaries

After some crashes in the 3D engine (!) on the Samsung GT-I8530
it turns out that the main firmware file can be device dependent,
something that was previously only handled for the NVRAM
parameter file.

Rewrite the code a bit so we can a per-board suffixed firmware
binary as well, if this does not exist we fall back to the
canonical firmware name.

Example: a 4330 device with the OF board compatible is
"samsung,gavini". We will first try
"brcmfmac4330-sdio.samsung,gavini.bin" then "brcmfmac4330-sdio.bin"
if that does not work.

Cc: phone-devel@vger.kernel.org
Cc: newbyte@disroot.org
Cc: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210711231659.255479-1-linus.walleij@linaro.org