image-ktn-sparkle: Only depend on touchtest-emv if the machine has display support
This allows to build the image for headless devices that have not enabled meta-qt5. In case meta-qt5 is available it gets rid of the unneeded package.
Please note that touchtest-emv
might be missing for machine configs that
do not have screen
in MACHINE_FEATURES
although they have graphics support.
For these cases the machine config should be fixed.
Cc: @Maximilian @estoll