E24 core documentation missing

[pridolfi]

The current datasheet is missing documentation about the E24 RV32 co-processor: memory layout, control interface and bus interconnect method to the U74 core, as well as any other information necessary to work on a driver or kernel module aiming to load a custom firmware for this core.

[MichaelZhuxx]

@pridolfi please check it out with commit 4eec14d