iommu: Add Allwinner H6 IOMMU driver

The Allwinner H6 has introduced an IOMMU for a few DMA controllers, mostly
video related: the display engine, the video decoders / encoders, the
camera capture controller, etc.

The design is pretty simple compared to other IOMMUs found in SoCs: there's
a single instance, controlling all the masters, with a single address
space.

It also features a performance monitoring unit that allows to retrieve
various informations (per-master and global TLB accesses, hits and misses,
access latency, etc) that isn't supported at the moment.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/d122a8670361e36fc26b4ce2674a2223d30dc4cc.1589378833.git-series.maxime@cerno.tech


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