KANSAS CITY, Mo. — The best NFL quarterback rivalries over the years have carried a heavy dose of postseason drama. For instance, four of the five playoff meetings between Peyton Manning and Tom Brady happened in the AFC Championship Game. Brett Farve vs. Steve Young, Terry Bradshaw vs. Ken Stabler, and from the way-back machine, Otto Graham vs. Bobby Layne: They all met in multiple win-or-go-home showdowns. On Sunday in Buffalo, Patrick Mahomes and the Chiefs will square off against Josh Allen and the Buffalo Bills. It will be their third postseason encounter, and there should be many more to…