By WILL GRAVES PITTSBURGH — Andy Reid donned a Santa Claus suit in a giddy Kansas City Chiefs locker room on Christmas Day, then handed his team a present it increasingly looks like it deserves: home-field advantage throughout the AFC playoffs. How Reid managed to slide into the costume so quickly after Kansas City’s clinical 29-10 victory over the reeling Pittsburgh Steelers to lock up the top seed in the AFC for the fourth time in seven years is a mystery (though he hinted there’s an elf involved). How Reid’s team manages to pull away from the pack year after year is not. A lot of Patrick Mahomes.