command: Include a required header in command.h

This uses ARRAY_SIZE() but does not include the header file which declares
it. Fix this, so that command.h can be included without common.h

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>

include/command.h

@@ -25,6 +25,10 @@
 #endif
 
 #ifndef	__ASSEMBLY__
+
+/* For ARRAY_SIZE() */
+#include <linux/kernel.h>
+
 /*
  * Monitor Command Table
  */