[aes] Potential minor PRNG-related modifications for production

[vogelpi]

Description

Following the big PRNG change in #20852, there are some minor changes that we might want to implement, also based on the penetration testing results:

• The 8-bit buffers for the PRD input inside the DOM S-Boxes should be moved up in the hierarchy. Ideally it's placed inside the aes_cipher_core.sv module. This doesn't change SCA properties but it simplifies control. This further allows taking the randomness for masking the initial state input from the buffers rather than from the PRNG directly (might be glitchy). This should have a beneficial impact on SCA hardening (to be evaluated on FPGA).
• The PRNG should be advanced in every cycle (but not the FF-based buffers of course) to increase the noise level. This needs the change above.

This won't have a noticeable timing or area impact. I'm thus putting in M3.

[andreaskurth]

PR #22844, which will resolve this, is currently under review.