libfdt: Add functions to get/add/delete memory reservemap entries

This patch adds functions to libfdt for accessing the memory
reservation map section of a device tree blob.  fdt_num_mem_rsv()
retreives the number of reservation entries in a dtb, and
fdt_get_mem_rsv() retreives a specific reservation entry.
fdt_add_mem_rsv() adds a new entry, and fdt_del_mem_rsv() removes a
specific numbered entry.

Testcases for these new functions are also included.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/run_tests.sh

@@ -31,6 +31,7 @@ tree1_tests () {
     TREE=$1
 
     # Read-only tests
+    run_test get_mem_rsv $TREE
     run_test root_node $TREE
     run_test find_property $TREE
     run_test subnode_offset $TREE