staging: wilc1000: handle add beacon operation callback from cfg80211 context

Refactor add/change beacon cfg80211 operation callback to handle from
cfg context. Also avoided extra copy of information by packing directly
in firmware expected format.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>