drm: Move drm_set_preferred_mode() helper from drm_edid to drm_modes

The helper is generic, it doesn't use the opaque EDID type struct drm_edid
and is also used by drivers that only support non-probeable displays such
as fixed panels.

These drivers add a list of modes using drm_mode_probed_add() and then set
a preferred mode using the drm_set_preferred_mode() helper.

It seems more logical to have the helper definition in drm_modes.o instead
of drm_edid.o, since the former contains modes helper while the latter has
helpers to manage the EDID information.

Since both drm_edid.o and drm_modes.o object files are built-in the drm.o
object, there are no functional changes. But besides being a more logical
place for this helper, it could also allow to eventually make drm_edid.o
optional and not included in drm.o if only fixed panels must be supported
in a given system.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240102122208.3103597-1-javierm@redhat.com