On the DRM backend, if an output is dpms'd off and a different output is
hotplugged, the CRTC for the output is reclaimed. When modesetting an
output without a CRTC, a CRTC will not be given to an output that is not
desired to be enabled. This splits setting the dpms state in
apply_output_config. If the output should be dpms on, the it is enabled
before attempting to modeset. Otherwise, it is dpms'd off after setting
everything else.
This also adds DPMS_ON to the default output configs.