staging: brcm80211: clean up firmware download code in fullmac

In brcmfmac the firmware download related code scatter all around.
And some old dead code which is not following the standard firmware
routine is still present. This patch limits the firmware download
related code only in dhd_sdio.c and removes the rest.

Signed-off-by: Franky Lin <frankyl@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>