drm/mgag200: Add struct mgag200_device_info

While currently empty, struct mgag200_device_info, will provide static,
constant information on each device model.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220601112522.5774-7-tzimmermann@suse.de