ecore_drm2: Fix mouse pointer when using absolute coords

ecore_drm2: Fix mouse pointer when using absolute coords

Running E wl2 in KVM led to the following issue: integrated mouse
pointer would always be stuck at (0,0).

The reason was that calibration would never happen, and it's
required* for absolute pointing devices, such as the qemu mouse
integration.

Fix: Listen to device add and calibrate based on the first
output. No idea if we could calibrate on any other output,
or how this should be done in case of multiple screens.

[*] I believe calibration might actually not be required, as
    the absolute position is already the correct one when
    received from libinput.