The mainly changes is below:
- Update scatter file, linker file for bootloader support
- Update the file for RZ/A1 serial flash boot loader
- Add "device name" and "bootloader_supported" in targets.json

In "targets/TARGET_RENESAS" 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.
- "targets/TARGET_RENESAS" folder
  <before>
  \targets\TARGET_RENESAS\TARGET_RZ_A1H
  \targets\TARGET_RENESAS\TARGET_VK_RZ_A1H
  <after>
  \targets\TARGET_RENESAS\TARGET_RZ_A1XX