[fix] CFI check for TRNG source

[mhatrevi]

This fix addresses the following issues:

1. Triple-verify TRNG MMIO read at CFI initialization in rom_entry #920
2. Triple call CFI Counter reset when seeding the prng #921

[andreslagarcavilla]

Needs rebase, please.

Also: "The Caliptra ROM is frozen; changes that affect the binary
require approval from the TAC." -- yes approved. This seems noisy at this stage

[nickg-ca]

Does this address #922 ? I only noticed that when looking at the compiled assembly which calls ureg:: read_volatile_slice and compiler_builtins::mem::memcpy::memcpy, either of which could be glitched to trigger a buffer overflow. For what it's worth I'm somewhat less concerned about #922 than the other issues.

[korran]

Does this address #922 ? I only noticed that when looking at the compiled assembly which calls ureg:: read_volatile_slice and compiler_builtins::mem::memcpy::memcpy, either of which could be glitched to trigger a buffer overflow. For what it's worth I'm somewhat less concerned about #922 than the other issues.

I don't think it does. I propose #989 to solve #922.