An example of an IP block on an SOC would be an ethernet PHY - the silicon gates needed to provide ethernet functionality directly from the SOC chip, and not from an external chip. In this context, "included" may have been a better word than "supported". That is, an SOC will often include several collections of (mostly predefined) silicon gates to provide specific hardware functions from the SOC.
SOC manufacturers often license or purchase IP blocks to add to their chips from external parties. Often, a spec. sheet for an SOC will say that a chip has a particular functionality, but not describe the hardware in enough detail to easily write a driver or adapt an existing one. Because many of these IP blocks come from the same vendors, it can save a lot of work if a driver author knows the source of the IP block on the SOC, as the developer can then reuse an existing driver, if there is one, more easily.