render/allocator: use render node if available in reopen_drm_node
render/allocator: use render node if available in reopen_drm_node

If we aren't trying to create a dumb buffer allocator, and if the
DRM device has a render node (ie, not a split render/display SoC),
then we can use the render node instead of the primary node. This
should allow wlroots to run under seatd when the current user
doesn't have the permission to open primary nodes (logind has a
quirk to allow physically logged in users to open primary nodes).

swaywm/wlroots,SirCmpwn/wlroots,swaywm/wlroots