The newest BSP for i.MX6ULL-EVK is L4.9.11_1.0.0, all the i.MX6ULL-EVK board materials are here MCIMX6ULL-EVK|i.MX6ULL Evaluation Kit|NXP . About how to build and download the BSP you can refer to the document i.MX_Yocto_Project_User's_Guide in nxp website.