The actual problem/bug is that for some reason the mainline Ubuntu 4.7 kernel lacks CONFIG_TOUCHSCREEN_ELAN. In 4.4 Ubuntu kernel CONFIG_TOUCHSCREEN_ELAN is defined, but the touchscreen doesn't work.
However with mainline Ubuntu kernel sources, and CONFIG_TOUCHSCREEN_ELAN enabled manually via a recompilation, touch screen now works! That means the touchscreen does work with mainline kernel but Ubuntu config is wrong for 4.7.
The actual problem/bug is that for some reason the mainline Ubuntu 4.7 kernel lacks CONFIG_ TOUCHSCREEN_ ELAN. In 4.4 Ubuntu kernel CONFIG_ TOUCHSCREEN_ ELAN is defined, but the touchscreen doesn't work.
However with mainline Ubuntu kernel sources, and CONFIG_ TOUCHSCREEN_ ELAN enabled manually via a recompilation, touch screen now works! That means the touchscreen does work with mainline kernel but Ubuntu config is wrong for 4.7.