staging: brcm80211: move utility functions into new module

Move utility functions shared by the brcmsmac and brcmfmac drivers into a new
module, brcmutil.ko.  This eliminates the need to compile and link the shared
functions into both drivers.  Prefix all exported symbols with "bcm_".

Cc: devel@linuxdriverproject.org
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Brett Rudley <brudley@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>