trusty: storage: proxy: FS_READY property setting on vendor only

Bug: 367965796
Test: launch_cvd --noresume --console=true \
      --extra_kernel_cmdline='androidboot.selinux=permissive' \
      --secure_hals=guest_keymint_trusty_insecure
Change-Id: I4d5ea1762f7cf9edfd8cbc00e2aec13caae965f4