In this sentence "what has come to be" means "what has become". Saying that something has "come to be" means that it has acquired a trait over time, in this context implying that Mrs. Thatcher believed in the ideas behind privatization before that set of ideas had the name "privatization".

what has come to be known as privatization. >as something that we now called privatization

It means that it is known now as 'privatization' , before it was not known as this.