of: Move of_skipped_node_table within #ifdef CONFIG_OF_ADDRESS

The `struct of_skipped_node_table` is used only when CONFIG_OF_ADDRESS
is defined, move it within the #ifdef/#endif to avoid warnings on
configurations where CONFIG_OF_ADDRESS isn't defined.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202308212037.YopffWSU-lkp@intel.com/
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lore.kernel.org/r/73dea4f4b389359a8beadbc77b00eb26853f9ab5.1692691032.git.viresh.kumar@linaro.org
Signed-off-by: Rob Herring <robh@kernel.org>