common: command: Add support for $ auto-completion

Add the dollar_complete() function to auto-complete arguments starting
with a '$' and use it in the cmd_auto_complete() path such that all
args starting with a $ can be auto-completed based on the available env
vars.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
[trini: Fix some linking problems]
Signed-off-by: Tom Rini <trini@konsulko.com>

include/common.h

@@ -248,7 +248,8 @@ static inline int env_set_addr(const char *varname, const void *addr)
 }
 
 #ifdef CONFIG_AUTO_COMPLETE
-int env_complete(char *var, int maxv, char *cmdv[], int maxsz, char *buf);
+int env_complete(char *var, int maxv, char *cmdv[], int maxsz, char *buf,
+		 bool dollar_comp);
 #endif
 int get_env_id (void);