I'm not sure if you are going to find any code provision that requires a certain bearing length onto masonry. However, other checks may govern the length of bearing such as bearing stresses, the capability of the masonry structure to support the eccentric load from a small bearing length, and the anchorage of said structural steel to masonry. A few places to check would be the Masonry Standards Joint Committee (MSJC) if in the U.S. Also, the attached website could have some valuable information.