brcmfmac: support STA info struct v7

The newest firmwares provide STA info using v7 of the struct. As v7
isn't backward compatible, a union is needed.

Even though brcmfmac does not use any of the new info it's important to
provide the proper struct buffer. Without this change new firmwares will
fallback to the very limited v3 instead of something in between such as
v4.

Signed-off-by: Dan Haab <dan.haab@luxul.com>
Reviewed-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>