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>
diff --git a/board/vscom/baltos/board.c b/board/vscom/baltos/board.c
index d3b1f15..5f730b8 100644
--- a/board/vscom/baltos/board.c
+++ b/board/vscom/baltos/board.c
@@ -68,7 +68,7 @@
 	printf("DIPs: 0x%1x\n", (~dips) & 0xf);
 
 	if ((dips & 0xf) == 0xe)
-		setenv("console", "ttyUSB0,115200n8");
+		env_set("console", "ttyUSB0,115200n8");
 
 	return 0;
 }
@@ -373,7 +373,7 @@
 		return -ENODEV;
 	}
 
-	setenv("board_name", model);
+	env_set("board_name", model);
 #endif
 
 	return 0;