evdev: warn about missing input devices
evdev: warn about missing input devices

Usually there should be at least one input device, when Weston starts
up, or is reactivated by a VT switch. Add a nice warning, in case there
are no input devices.

This is to give a clue to users who happen to try Weston on DRM, and
do not get any response.

Add also a message to another failure case, that may lead to missing
input devices.

Signed-off-by: Pekka Paalanen <6c0263d81461c956d504307112a4ce25eaacc3d1@gmail.com>

jonnylamb/weston,mchalupa/weston,Gnurou/weston,Tarnyko/weston-xdg_surface_present,Gnurou/weston,krezovic/weston,giucam/weston,sir-murray/weston,sir-murray/weston,kwm81/weston,eyolfson/weston,krezovic/weston,udoprog/weston,udoprog/weston,Fantu/compositor-spice,Tarnyko/weston-xdg_surface_present,giucam/weston,eyolfson/weston,xorgy/weston,Fantu/compositor-spice,Fantu/compositor-spice,mchalupa/weston,kwm81/weston,xorgy/weston,jonnylamb/weston