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/drivers/fastboot/fb_common.c b/drivers/fastboot/fb_common.c
index e76af8e..c3735a4 100644
--- a/drivers/fastboot/fb_common.c
+++ b/drivers/fastboot/fb_common.c
@@ -11,6 +11,7 @@
  */
 
 #include <common.h>
+#include <command.h>
 #include <env.h>
 #include <fastboot.h>
 #include <net/fastboot.h>