init.h: Add "struct cmd_tbl"

In order to avoid needing to add <command.h> to this file, add "struct
cmd_tbl" before the prototype for do_bdinfo().

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/init.h b/include/init.h
index 630d867..2c10171 100644
--- a/include/init.h
+++ b/include/init.h
@@ -401,6 +401,8 @@
 /* Show arch-specific information for the 'bd' command */
 void arch_print_bdinfo(void);
 
+struct cmd_tbl;
+
 int do_bdinfo(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[]);
 
 #endif	/* __ASSEMBLY__ */