arm: mach-omap2: remove NULL board_mux from board files

If CONFIG_OMAP_MUX is not enabled, we can define board_mux in the header
file instead of forcing every single board to define it.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
[tony@atomide.com: updated for combined board-zoom files]
Signed-off-by: Tony Lindgren <tony@atomide.com>
diff --git a/arch/arm/mach-omap2/mux.h b/arch/arm/mach-omap2/mux.h
index 79076d6..f5f7f49 100644
--- a/arch/arm/mach-omap2/mux.h
+++ b/arch/arm/mach-omap2/mux.h
@@ -172,6 +172,8 @@
 	return 0;
 }
 
+static struct omap_board_mux *board_mux __initdata __maybe_unused;
+
 #endif
 
 /**