dri3: Rework of the xcb connection

. Remove the Xlib calls by Xcb ones
. Use two xcb connections to avoid libxcb threading bugs

Signed-off-by: Axel Davy <axel.davy@ens.fr>
fix small typo

Signed-off-by: Axel Davy <axel.davy@ens.fr>
Trivial typo fixes