ARM: keystone: remove unnecessary prom.h include

Remove unnecessary prom.h include in preparation to make prom.h optional.
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Grant Likely <grant.likely@linaro.org>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>

arch/arm/mach-keystone/platsmp.c

@@ -17,7 +17,6 @@
 #include <linux/io.h>
 
 #include <asm/smp_plat.h>
-#include <asm/prom.h>
 
 #include "keystone.h"