Fix a regression with VT-switching away from Weston and then back
causing drmModePageFlip() to fail with ENOSPC or EINVAL, leaving one or
more outputs not updated. The regression appeared in
47224cc9:

	compositor-drm: Delete drm_backend_set_modes

Fix it by forcing a drmModeSetCrtc() on all outputs both initially
created and after VT-switch in.

Cc: Daniel Stone <daniels@collabora.com>
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

v2: moved state_invalid=true from create_output_for_connector() to
    drm_output_enable()

Reviewed-by: Daniel Stone <daniels@collabora.com>