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_command.c b/drivers/fastboot/fb_command.c
index 4864344..3c4acfe 100644
--- a/drivers/fastboot/fb_command.c
+++ b/drivers/fastboot/fb_command.c
@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <command.h>
 #include <env.h>
 #include <fastboot.h>
 #include <fastboot-internal.h>