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/board/grinn/liteboard/board.c b/board/grinn/liteboard/board.c
index 1558ea4..151041a 100644
--- a/board/grinn/liteboard/board.c
+++ b/board/grinn/liteboard/board.c
@@ -4,6 +4,7 @@
  * Copyright (C) 2016 Grinn
  */
 
+#include <command.h>
 #include <asm/arch/clock.h>
 #include <asm/arch/iomux.h>
 #include <asm/arch/imx-regs.h>