sparc: Move 'unique_id' into prom_common.c and rename to 'prom_unique_id'

This will be used in a subsequent changeset.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/arch/sparc/kernel/prom_common.c b/arch/sparc/kernel/prom_common.c
index ded8c62..a231808 100644
--- a/arch/sparc/kernel/prom_common.c
+++ b/arch/sparc/kernel/prom_common.c
@@ -119,3 +119,4 @@
 }
 EXPORT_SYMBOL(of_find_in_proplist);
 
+unsigned int prom_unique_id;