dt-bindings: iommu: riscv: Add bindings for RISC-V IOMMU

Add bindings for the RISC-V IOMMU device drivers.

Co-developed-by: Anup Patel <apatel@ventanamicro.com>
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Tomasz Jeznach <tjeznach@rivosinc.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Link: https://lore.kernel.org/r/6c255602e296feaf0f005b498de4e6fdf8686ff7.1729059707.git.tjeznach@rivosinc.com


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