btrfs-progs: help: define helper for command with flags

Add macro to define a simple command that also gets some non-default
flags, eg. the output formats.

Signed-off-by: David Sterba <dsterba@suse.com>

cmds/commands.h

@@ -88,6 +88,14 @@ struct cmd_struct {
 	DEFINE_COMMAND(name, token, cmd_ ##name,			\
 		       cmd_ ##name ##_usage, NULL, 0)
 
+/*
+ * Define a command with flags, eg. with the additional output formats.
+ * See CMD_* .
+ */
+#define DEFINE_COMMAND_WITH_FLAGS(name, token, flags)			\
+	DEFINE_COMMAND(name, token, cmd_ ##name,			\
+		       cmd_ ##name ##_usage, NULL, (flags))
+
 /*
  * Define a command group callback.
  * It's assumed that the callback is called cmd_<name> and the