It isn’t easy to find white space in the world of venture capital, where every venture firm must have a specific vision to sell to the universities, pension funds and family offices that tend to fund them. But Brendan Wallace and business partner Brad Greiwe have a fresh pitch, as well as nontraditional investors. Their L.A.-based venture firm, Fifth Wall Ventures, invests in startups that are benefiting from changes in the real estate market, and they turned to the country’s largest real estate companies to fund it.