env: Rename common functions related to setenv()

We are now using an env_ prefix for environment functions. Rename these
commonly used functions, 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/common/board_r.c b/common/board_r.c
index a4a7384..016dc02 100644
--- a/common/board_r.c
+++ b/common/board_r.c
@@ -486,7 +486,7 @@
 	else
 		set_default_env(NULL);
 #ifdef CONFIG_OF_CONTROL
-	setenv_addr("fdtcontroladdr", gd->fdt_blob);
+	env_set_addr("fdtcontroladdr", gd->fdt_blob);
 #endif
 
 	/* Initialize from environment */