staging: brcm80211: remove code from pmu.c related to unsupported chipsets

The pmu source file contains several code fragments for chipsets that
are not supported by this driver. These have been removed.

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