drm/vkms: Allow to attach encoders and CRTCs

drm/vkms: Allow to attach encoders and CRTCs

Add a list of possible CRTCs to the encoder configuration and helpers to
attach and detach them.

Now that the default configuration has its encoder and CRTC correctly
attached, 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/20250218101214.5790-13-jose.exposito89@gmail.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>