The PICO-PI-IMX7 is a TechNexion board defined here. It is now supported in mainline U-Boot, mainline Kernel, FSL Community BSP and Buildroot.
In mainline U-Boot it is supported since v2017.07.
In mainline Linux Kernel it is supported since 4.13.
To generate an image for PICO-PI-IMX7 using FSL Community BSP, please see: The imx7d-pico board is now supported in FSL Community BSP - i.MXDev Blog.
To generate an image for PICO-PI-IMX7 using Buildroot, please see: The imx7d-pico board is now supported in Buildroot - i.MXDev Blog.