drm/ast: Add struct ast_connector

Add struct ast_connector to track a connector's physical status. With
the upcoming BMC support, the physical status can be different from the
reported status.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240815151953.184679-3-tzimmermann@suse.de