broadcom-nvram-config: add nvram file support

Add a recipe to provide an nvram file required by certain Broadcom wifi
chips.  This file is machine-specific.

Files are installed at /lib/firmware/brcm.
wandboard-dual: Add broadcom-nvram-support to machine

Adds a line MACHINE_EXTRA_RRECOMMENDS for broadcom-nvram-support which
provides firmware files for the wifi chip (BCM4329) on Wandboard Dual.