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/nokia/rx51/rx51.c b/board/nokia/rx51/rx51.c
index 3d019b0..6a4427a 100644
--- a/board/nokia/rx51/rx51.c
+++ b/board/nokia/rx51/rx51.c
@@ -421,7 +421,7 @@
 	/* reuse atags from previous bootloader */
 	reuse_atags();
 
-	dieid_num_r();
+	omap_die_id_display();
 	print_cpuinfo();
 
 	/*