Create extra symbolic links at root for arm64 GSI

Relevant firmware/SW components have been moved out of directories
under root, but not all references to them updated. For example,
/vendor/firmware_mnt won't be used by Android to load firmware.
So we still need these symlinks so the firmware/SW components can
be accesses.

These links should be removed after all references are updated.

Bug: 111287060
Test: $ lunch aosp_arm64-userdebug; m -j
      # Checked $OUT/root for the added links
Change-Id: Ia7915dbdeabdee7a5cf8851772e89f080b927c45