env: Rename the redundancy flags

Add an ENV prefix to these two flags so that it is clear what they relate
to. Also move them to env.h since they are part of the public API. Use an
enum rather than a #define to tie them together.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/env/sf.c b/env/sf.c
index 5531293..09646e1 100644
--- a/env/sf.c
+++ b/env/sf.c
@@ -30,8 +30,6 @@
 static ulong env_new_offset	= CONFIG_ENV_OFFSET_REDUND;
 #endif
 
-#define ACTIVE_FLAG	1
-#define OBSOLETE_FLAG	0
 #endif /* CONFIG_ENV_OFFSET_REDUND */
 
 DECLARE_GLOBAL_DATA_PTR;
@@ -74,7 +72,7 @@
 static int env_sf_save(void)
 {
 	env_t	env_new;
-	char	*saved_buffer = NULL, flag = OBSOLETE_FLAG;
+	char	*saved_buffer = NULL, flag = ENV_REDUND_OBSOLETE;
 	u32	saved_size, saved_offset, sector;
 	int	ret;
 
@@ -85,7 +83,7 @@
 	ret = env_export(&env_new);
 	if (ret)
 		return -EIO;
-	env_new.flags	= ACTIVE_FLAG;
+	env_new.flags	= ENV_REDUND_ACTIVE;
 
 	if (gd->env_valid == ENV_VALID) {
 		env_new_offset = CONFIG_ENV_OFFSET_REDUND;