brcmfmac: add support for bus specific data command

brcmfmac need to support data command setting for dongle's bus
core. A list must be placed at brcmf_bus structure before calling
brcmf_bus_start in order to be sent by brcmf_c_preinit_dcmds.

Reviewed-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>