staging: brcm80211: move fullmac watchdog timer code to dhd_sdio.c

The watchdog timer is used in bus interface layer in fullmac. Move
related code to dhd_sdio.c for clean up.

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>