Fix up (run) depends of devel/libmtdev

There's some confusion about evdev headers, and this patch
was shunted back and forth between Qt and others for a while,
and then languished.

Original patch from Ting-Wei Lan, partly obsoleted by changes
in Qt in ports r514242 and r514255, OK'ed by maintainer in the PR.

PR: 240964
Submitted by: Ting-Wei Lan
Reported by: Walter Schwarzenfeld
Reviewed by: adridg
Approved by: hselasky