lib: utils/fdt: Change addr and size to uint64_t

The maximum address and size encoded in DT are 64-bit numbers, so we
should use uint64_t for 'addr' and 'size' in fdt_get_node_addr_size().

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>