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/isee/igep003x/board.c b/board/isee/igep003x/board.c
index e33170d..24687e2 100644
--- a/board/isee/igep003x/board.c
+++ b/board/isee/igep003x/board.c
@@ -194,13 +194,13 @@
 #ifdef CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG
 	switch (get_board_revision()) {
 		case 0:
-			setenv("board_name", "igep0034-lite");
+			env_set("board_name", "igep0034-lite");
 			break;
 		case 1:
-			setenv("board_name", "igep0034");
+			env_set("board_name", "igep0034");
 			break;
 		default:
-			setenv("board_name", "igep0033");
+			env_set("board_name", "igep0033");
 			break;
 	}
 #endif