staging: brcm80211: cleanup function prototypes in header files

Several header files were specifying function prototypes although
no other module was relying on them. They have been moved to the
related source file and made static or removed if the functions
were non-existent in the driver.

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>