Updated sections in RVFI documentation to reflect the expansion of rv…

Created by: silabs-oysteink

…fi_mem and the addition of rvfi_gpr signals. Added paragraph on the special reporting of the mnxti CSR on RVFI.

Updated RVFI memory reporting to be in line with user manual for split misaligned transfers.

Signed-off-by: Oystein Knauserud Oystein.Knauserud@silabs.com