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/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index f192ca5..1a65a3f 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -682,7 +682,7 @@
 
 	printf("Found %d device(s).\n", scsi_max_devs);
 #ifndef CONFIG_SPL_BUILD
-	setenv_ulong("scsidevs", scsi_max_devs);
+	env_set_ulong("scsidevs", scsi_max_devs);
 #endif
 	return 0;
 }