drm/vkms: Allow to configure multiple planes

drm/vkms: Allow to configure multiple planes

Add a list of planes to vkms_config and create as many planes as
configured during output initialization.

For backwards compatibility, add one primary plane and, if configured,
one cursor plane and NUM_OVERLAY_PLANES planes to the default
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/20250218101214.5790-9-jose.exposito89@gmail.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>