[edn, doc, rom] EDN documentation requires updates

@moidx is already working on this.

Since Apr 1, 2024.

### Description

[Boot-time Request Mode](https://opentitan.org/book/hw/ip/edn/doc/theory_of_operation.html#boot-time-request-mode) doc states:
"In boot-time request mode, the command sequence is fully hardware-controlled and no command customization is possible. In this mode, the EDN automatically issues a special reduced-latency instantiate command followed by the default generate commands. This means, for instance, that no personalization strings or additional data may be passed to the CSRNG application interface port in this mode. On exiting, the EDN issues an uninstantiate command to destroy the associated CSRNG instance."

1. Does it mean that after boot mode is completed, nothing is using EDN unless explicitly requested? and as such,
2. Can EDN be left completely disabled after boot-time to reduce power consumption? Any implications of it?
3. What HW is using EDN and in what cases?
4. What would happen if CSRNG is disabled, but EDN is enabled in violation to [module enable and disable](https://opentitan.org/book/hw/ip/edn/doc/programmers_guide.html#module-enable-and-disable). I suppose EDN won't receive acknowledgment, but how to recover? Disable it, enable CSRNG, enable EDN?
5. What specifically ROM does in regards to EDN use, and any guidance/assumptions for what ROM_EXT should do.
6. Why [Auto Request Mode](https://opentitan.org/book/hw/ip/edn/doc/theory_of_operation.html#auto-request-mode) is not a default? It seems that EDN can function with minimal control from firmware.
7. Why would firmware prefer to use [GENERATE_CMD](https://opentitan.org/book/hw/ip/edn/doc/registers.html#generate_cmd--generate_cmd) when it seems that EDN will issue these commands as needed in auto request mode? How many commands shall be written and why?
8. Overall [Programmers guide](https://opentitan.org/book/hw/ip/edn/doc/programmers_guide.html) requires more details .

@vogelpi , @h-filali ?