omap-common: Common function to display die id, replacing omap3-specific version

This introduces omap_die_id_display to display the full die id.
There is no need to store it in an environment variable, that no boot script
is using anyway.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/board/ti/evm/evm.c b/board/ti/evm/evm.c
index 3f93d9c..ff3971d 100644
--- a/board/ti/evm/evm.c
+++ b/board/ti/evm/evm.c
@@ -159,7 +159,7 @@
 #if defined(CONFIG_CMD_NET)
 	reset_net_chip();
 #endif
-	dieid_num_r();
+	omap_die_id_display();
 
 	return 0;
 }