wifi: brcmfmac: firmware: Handle per-board clm_blob files

Teach brcm_alt_fw_paths to correctly split off variable length
extensions, and enable alt firmware lookups for the CLM blob firmware
requests.

Apple platforms have per-board CLM blob files.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Hector Martin <marcan@marcan.st>
Reviewed-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/E1oZDnT-0077a4-4k@rmk-PC.armlinux.org.uk