Hello Dan,
There are two ways to see the g2d test source,
1. If you have the vivante license to have vivante gpu source code, you can see the code in gpu-viv(5)/fsl_drv/g2d, there are scripts to build the g2d_test and g2d_overlay_test.
2. If you don't have the license to have vivante gpu source code, the g2d_test and g2d_overlay_test have been integrated into new demo framework. It is the C++ framework, but g2d_test and g2d_overlay_test keeps the same as in driver, they just have C++ wrap. The code is in /your yocto directory build director something like
/yocto-ga-wayland/build-wayland/tmp/work/cortexa9hf-vfp-neon-mx6qdl-poky-linux-gnueabi/fsl-gpu-sdk/2.2.1-r0/fsl-gpu-sdk-2.2.1/DemoApps/G2D
There are detailed instruction to build these apps stand alone in yocto-ga-wayland/build-wayland/tmp/work/cortexa9hf-vfp-neon-mx6qdl-poky-linux-gnueabi/fsl-gpu-sdk/2.2.1-r0/fsl-gpu-sdk-2.2.1/Doc/Setup_guide_yocto.txt
Regards