env: Rename setenv() to env_set()

We are now using an env_ prefix for environment functions. Rename setenv()
for consistency. Also add function comments in common.h.

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

include/configs/tam3517-common.h

@@ -334,7 +334,7 @@ do {								\
 		else						\
 			strcpy(ethname, "ethaddr");		\
 		printf("Setting %s from EEPROM with %s\n", ethname, buf);\
-		setenv(ethname, buf);				\
+		env_set(ethname, buf);				\
 	}							\
 } while (0)