LogFunctionNames performance by

[JoarGjersund]

as mentioned in renode/renode#330, we should mention the use of cpu LogTranslationBlockFetch true as an alternative to cpu LogFunctionNames true for improving performance when logging function names.

[pgielda]

LogFunctionNames will log when the function actually is executed. LogTranslationBlockFetch will only log when the block is first fetched and translated and will not log subsequently if the block is executed from cache and not retranslated. Very often LogTranslationBlockFetch is the good first approximation but its not a "true" trace.