drm/rockchip: Use fbdev-dma

Implement fbdev emulation with fbdev-dma. Fbdev-dma now supports
damage handling, which is required by rockchip. Avoids the overhead of
fbdev-generic's additional shadow buffering. No functional changes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Sandy Huang <hjc@rock-chips.com>
Cc: "Heiko Stübner" <heiko@sntech.de>
Cc: Andy Yan <andy.yan@rock-chips.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240419083331.7761-32-tzimmermann@suse.de