brcmfmac: provide firmware version in ethtool driver info

Knowing the firmware version is pretty useful information when
looking at issues. It is retrieved during initialization so
store it in driver data structure to fill the ethtool driver
info when requested.

Reviewed-by: Hante Meuleman <meuleman@brodcom.com>
Reviewed-by: Franky Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>