Reland "unpack_bootimg: Create symlink as alternate vendor ramdisk names" am: a08985e112 am: fd6c83c7c4

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/1669629

Change-Id: I63e97d1e27f7696ce89d5a0e83c2d715088b5dd8