iommu: rockchip: Add internal ops to handle variants

Add internal ops to be able to handle incoming variant v2.
The goal is to keep the overall structure of the framework but
to allow to add the evolution of this hardware block.

The ops are global for a SoC because iommu domains are not
attached to a specific devices if they are for a virtuel device like
drm. Use a global variable shouldn't be since SoC usually doesn't
embedded different versions of the iommu hardware block.
If that happen one day a WARN_ON will be displayed at probe time.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20210604164441.798362-4-benjamin.gaignard@collabora.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>