drm/vkms: Allow to attach connectors and encoders

drm/vkms: Allow to attach connectors and encoders

Add a list of possible encoders to the connector configuration and
helpers to attach and detach them.

Now that the default configuration has its connector and encoder
correctly, configure the output following the configuration.

Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Co-developed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250218101214.5790-15-jose.exposito89@gmail.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>