The Qt Enterprise Embedded is a commercial version of Qt for embedded devices If you need support you can buy it from Digia.
The Qt libraries 4.8.5 for embedded Linux is also available for download. It uses Compact and Efficient Windowing System (QWS). It writes directly to the Linux framebuffer, eliminating the need for the X11 windowing system and saving memory.
You can use Qt5 for embedded devices as long as you have a good graphics stack. There is no specific Embedded prebuild available for Qt5 because QWS was dropped in favour for Qt Platform Abstraction. So, Qt does not ship with a windowing system anymore, it expects the OS to provide one (or at least some display devices like directFB etc.).