memrange: add 2 new range_entry routines

Two convenience functions are added to operate on a range_entry:
- range_entry_update_tag() - update the entry's tag
- memranges_next_entry() - get the next entry after the one provide

These functions will be used by a follow on patch to the MTRR code
to allow hole punching in WB region when the default MTRR type is
UC.

Change-Id: I3c2be19c8ea1bbbdf7736c867e4a2aa82df2d611
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/2924
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/lib/memrange.c

@@ -321,3 +321,9 @@ void memranges_fill_holes_up_to(struct memranges *ranges,
 	/* Merge all entries that were newly added. */
 	merge_neighbor_entries(ranges);
 }
+
+struct range_entry *memranges_next_entry(struct memranges *ranges,
+                                         const struct range_entry *r)
+{
+	return r->next;
+}