ARM: OMAP2+: Legacy support for wl12xx when booted with devicetree

Without WLAN we cannot switch omap4 to use device tree
only booting. This patch can be reverted when the
binding for wl12xx is added.

Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Rajendra Nayak <rnayak@ti.com>
Cc: devicetree-discuss@lists.ozlabs.org
Tested-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>