Enable tslib autodetection in configure

Change-Id: I4adbae621e4baa3a24e22a5b5832a08edfab377e
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Andy Nichols <andy.nichols@digia.com>
Simplify using tslib with eglfs

tslib support can now be built-in into eglfs, like evdev.

Set QT_QPA_EGLFS_TSLIB to 1 to use tslib instead of evdevtouch.

The input device can be controlled via TSLIB_TSDEVICE.

Change-Id: Iff6bdbb4d133f73eca5528705844862236f8752b
Reviewed-by: Andy Nichols <andy.nichols@digia.com>