common: Move command functions out of common.h

Move these functions into the command.h header file which is a better fit.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/sandbox/cpu/start.c b/arch/sandbox/cpu/start.c
index cfc542c..fff9cbd 100644
--- a/arch/sandbox/cpu/start.c
+++ b/arch/sandbox/cpu/start.c
@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <command.h>
 #include <errno.h>
 #include <os.h>
 #include <cli.h>