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/keymile/km83xx/km83xx.c b/board/keymile/km83xx/km83xx.c
index 8020c37..5e07faa 100644
--- a/board/keymile/km83xx/km83xx.c
+++ b/board/keymile/km83xx/km83xx.c
@@ -263,11 +263,11 @@
 	mv88e_sw_reset(name, CONFIG_KM_MVEXTSW_ADDR);
 
 	if (piggy_present()) {
-		setenv("ethact", "UEC2");
-		setenv("netdev", "eth1");
+		env_set("ethact", "UEC2");
+		env_set("netdev", "eth1");
 		puts("using PIGGY for network boot\n");
 	} else {
-		setenv("netdev", "eth0");
+		env_set("netdev", "eth0");
 		puts("using frontport for network boot\n");
 	}
 #endif
@@ -280,7 +280,7 @@
 	if (dip_switch != 0) {
 		/* start bootloader */
 		puts("DIP:   Enabled\n");
-		setenv("actual_bank", "0");
+		env_set("actual_bank", "0");
 	}
 #endif
 	set_km_env();