Daniel Stone authored Mar 01, 2017 and Pekka Paalanen committed Mar 14, 2017

In preparation for grouping output repaint together where possible,
switch the per-output repaint timer, to a global timer which iterates
across all outputs.

This is implemented by storing the absolute time for the next repaint
for each output locally, and maintaining a global timer which iterates
all of them, scheduling the repaint for the first available time.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
[Pekka: The comment about 1 ms delay.]
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>