IDEVID CSR Envelope is not initialized

[Neal-liu]

Caliptra version: 2.1

When I try to extract IDEVID CSR envelope through mailbox at Caliptra ROM stage, the Envelope data structure seems not be initialized.
The marker and size is 0, only ecc_csr, mldsa_csr, and csr_mac has value.

This persistent data storage only initializes when generation CSR flags is not asserted.