Rap’s Cheech and Chong, Snoop Dogg and Wiz Khalifa, drink, smoke, and live easy on their carefree collaboration “Young, Wild & Free,” the first offering from the soundtrack to their stoner comedy Mac and Devin Go to High School, due in early 2012. Hip-hop’s favorite accessory Bruno Mars lays down a breezy hook over the piano-driven melody. Blaze up their new joint.