Qt developer Laszlo Agocs has written a lengthy blog post about building the Qt5 dev branch for Android AArch64. His guide was done with a NVIDIA Shield TV. Thanks to using the Qt dev branch and the Tegra X1 SoC having Vulkan drivers, he was able to even show off Qt's forthcoming Vulkan enablement work.
As covered a few days ago, initial Vulkan integration is coming to Qt 5.10 later this year while currently it's available via the "dev" branch.
If you are curious about building Qt for Android devices for testing or experiments, Laszlo's guide is great for a complete walk-through of the process along with OpenGL and Vulkan examples.
Those interested in learning more can stop by the Qt blog.