drm/ast: Detect ast device type and config mode without ast device

Return the ast chip and config in the detection function's parameters
instead of storing them directly in the ast device instance.

v2:
	* add break statements to switch default branches (Jocelyn)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231116100240.22975-10-tzimmermann@suse.de