Commonize RZ_A1 related folders placed in "FEATURE_LWIP" directory

In the below "features/FEATURE_LWIP" folders, same as Cortex-M targets, I changed the folder structure to combine files that can be shared as RZ/A1 related. And I renamed the folder name to "TARGET_RZ_A1XX" in order to make commonality explicit.
- "features/FEATURE_LWIP" folder
  <before>
  \features\FEATURE_LWIP\lwip-interface\lwip-eth\arch\TARGET_RZ_A1H
  \features\FEATURE_LWIP\lwip-interface\lwip-eth\arch\TARGET_VK_RZ_A1H
  <after>
  \features\FEATURE_LWIP\lwip-interface\lwip-eth\arch\TARGET_RZ_A1XX

Author: TomoYamanaka