drm/mgag200: Remove struct mga_connector

struct mga_connector has outlived its purpose. Inline the rsp init
helper into the mode-config code and remove the data structure. No
functional changes.

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/20220516134343.6085-6-tzimmermann@suse.de