staging: brcm80211: move driver variable functions to srom.c

The driver uses variables which are stored in string format. Using
strings as variable identifiers is disliked by the community. The
driver has been cleaned up and the only module providing these
variables is srom.c. The variable retrieval functions have been
moved to srom.c in preparation of a more likable way to store and
lookup these driver variables.

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Alwin Beukers <alwin@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>