drm: DPMS is no longer the only mutable connector prop

There are a bunch of other writable connector properties now.

Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Cc: Michel Dänzer <michel@daenzer.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/vrfq3PQ_YaPv75xE6-4QeyyLkevKNLpQo8JgnX6EnEcYaFRXxSg98QECUOmHe_eMirwPB0qNRXHE_jzEkXDb3J3YS2OuZXAZgJFnNMLm6W4=@emersion.fr