env: Rename some other getenv()-related functions

We are now using an env_ prefix for environment functions. Rename these
other functions as well, for consistency:

   getenv_vlan()
   getenv_bootm_size()
   getenv_bootm_low()
   getenv_bootm_mapsize()
   env_get_default()

Suggested-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Simon Glass <sjg@chromium.org>

include/common.h

@@ -749,7 +749,7 @@ int zzip(void *dst, unsigned long *lenp, unsigned char *src,
 
 /* lib/net_utils.c */
 #include <net.h>
-static inline struct in_addr getenv_ip(char *var)
+static inline struct in_addr env_get_ip(char *var)
 {
 	return string_to_ip(env_get(var));
 }