drm/fb-helper: Do not allocate unused apertures structure

The apertures field in struct fb_info is not used by DRM drivers. Do
not allocate it.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221219160516.23436-7-tzimmermann@suse.de