common: Fix-up MAC addr in dts by fetching env variable serially

The MAC addresses get fixed in the device tree for "ethernet" nodes
is by using trailing number behind "ethernet" found in "/aliases".
It may not be necessary for the "ethernet" nodes to be sequential.
There can be gaps in between or any node disabled

So provide a support to fetch MAC addr sequentially from env
and apply them to "ethernet" nodes in the order they appear in
device tree only if "ethernet" is not "disabled"

Signed-off-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>
diff --git a/README b/README
index 93c7ea9..53502c0 100644
--- a/README
+++ b/README
@@ -1603,6 +1603,15 @@
 
 		See doc/README.link-local for more information.
 
+ - MAC address from environment variables
+
+		FDT_SEQ_MACADDR_FROM_ENV
+
+		Fix-up device tree with MAC addresses fetched sequentially from
+		environment variables. This config work on assumption that
+		non-usable ethernet node of device-tree are either not present
+		or their status has been marked as "disabled".
+
  - CDP Options:
 		CONFIG_CDP_DEVICE_ID