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/qualcomm/dragonboard410c/dragonboard410c.c b/board/qualcomm/dragonboard410c/dragonboard410c.c
index 37d0b85..848e278 100644
--- a/board/qualcomm/dragonboard410c/dragonboard410c.c
+++ b/board/qualcomm/dragonboard410c/dragonboard410c.c
@@ -128,7 +128,7 @@
 	}
 
 	if (dm_gpio_get_value(&resin)) {
-		setenv("bootdelay", "-1");
+		env_set("bootdelay", "-1");
 		printf("Power button pressed - dropping to console.\n");
 	}