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/compulab/cm_t3517/cm_t3517.c b/board/compulab/cm_t3517/cm_t3517.c
index b33522e..d1c74db 100644
--- a/board/compulab/cm_t3517/cm_t3517.c
+++ b/board/compulab/cm_t3517/cm_t3517.c
@@ -101,7 +101,7 @@
 int misc_init_r(void)
 {
 	cl_print_pcb_info();
-	dieid_num_r();
+	omap_die_id_display();
 
 	return 0;
 }