iommu/riscv: Add RISC-V IOMMU platform device driver

Introduce platform device driver for implementation of RISC-V IOMMU
architected hardware.

Hardware interface definition located in file iommu-bits.h is based on
ratified RISC-V IOMMU Architecture Specification version 1.0.0.

This patch implements platform device initialization, early check and
configuration of the IOMMU interfaces and enables global pass-through
address translation mode (iommu_mode == BARE), without registering
hardware instance in the IOMMU subsystem.

Link: https://github.com/riscv-non-isa/riscv-iommu


Co-developed-by: Nick Kossifidis <mick@ics.forth.gr>
Signed-off-by: Nick Kossifidis <mick@ics.forth.gr>
Co-developed-by: Sebastien Boeuf <seb@rivosinc.com>
Signed-off-by: Sebastien Boeuf <seb@rivosinc.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Tomasz Jeznach <tjeznach@rivosinc.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Link: https://lore.kernel.org/r/2f2e4530c0ee4a81385efa90f1da932f5179f3fb.1729059707.git.tjeznach@rivosinc.com


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