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/bachmann/ot1200/ot1200.c b/board/bachmann/ot1200/ot1200.c
index 1ad4ef9..df10d6a 100644
--- a/board/bachmann/ot1200/ot1200.c
+++ b/board/bachmann/ot1200/ot1200.c
@@ -312,9 +312,9 @@
 
 	/* depending on the phy address we can detect our board version */
 	if (phydev->addr == 0)
-		setenv("boardver", "");
+		env_set("boardver", "");
 	else
-		setenv("boardver", "mr");
+		env_set("boardver", "mr");
 
 	printf("using phy at %d\n", phydev->addr);
 	ret = fec_probe(bis, -1, base, bus, phydev);