The method to define the pin mux has changed. As you point out, previously pin mux definition was handled in the board file, now it is handled using a method called device tree. The source files for the various evms that TI supports are defined in the arch/arm/boot/dts. These device tree source files now contain the information that used to be stored in the board file.
We are working on providing some better collateral to assist with develpoing device tree source files for TI catalog processors.
For the moment here is a link to help get started with understanding device tree at a generic level, towards the end of the wiki page are some good presentations:
One question usually asked is why the change, the reason is that the proliferation of ARM SOC and hence board files was impacting kernel migrations. Therefore Linux Community now will not allow any upstream support of an ARM SOC without the supporting drivers getting their platform data from a device tree.