iommu/riscv: Enable IOMMU registration and device probe.

Advertise IOMMU device and its core API.
Only minimal implementation for single identity domain type, without
per-group domain protection.

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Tomasz Jeznach <tjeznach@rivosinc.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Link: https://lore.kernel.org/r/ba79c8eb9c7f1cd9a8961a1b048e3991ee9a2b05.1729059707.git.tjeznach@rivosinc.com


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