wifi: brcmfmac: common: Add support for downloading TxCap blobs

The TxCap blobs are additional data blobs used on Apple devices, and
are uploaded analogously to CLM blobs. Add core support for doing this.

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>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230214092423.15175-8-marcan@marcan.st