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/siemens/common/factoryset.c b/board/siemens/common/factoryset.c
index 6c869ed..4e5ad58 100644
--- a/board/siemens/common/factoryset.c
+++ b/board/siemens/common/factoryset.c
@@ -266,7 +266,7 @@
 
 static struct ctrl_dev *cdev = (struct ctrl_dev *)CTRL_DEVICE_BASE;
 
-static int factoryset_mac_setenv(void)
+static int factoryset_mac_env_set(void)
 {
 	uint8_t mac_addr[6];
 
@@ -296,11 +296,11 @@
 	return 0;
 }
 
-int factoryset_setenv(void)
+int factoryset_env_set(void)
 {
 	int ret = 0;
 
-	if (factoryset_mac_setenv() < 0)
+	if (factoryset_mac_env_set() < 0)
 		ret = -1;
 
 	return ret;