iommu/riscv: Device directory management.

Introduce device context allocation and device directory tree
management including capabilities discovery sequence, as described
in Chapter 2.1 of the RISC-V IOMMU Architecture Specification.

Device directory mode will be auto detected using DDTP WARL property,
using highest mode supported by the driver and hardware. If none
supported can be configured, driver will fall back to global pass-through.

First level DDTP page can be located in I/O (detected using DDTP WARL)
and system memory.

Only simple identity and blocking protection domains are supported by
this implementation.

Co-developed-by: Nick Kossifidis <mick@ics.forth.gr>
Signed-off-by: Nick Kossifidis <mick@ics.forth.gr>
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/e1c763aeccd2c05fd4ad3a32f6f2ff3b3148d907.1729059707.git.tjeznach@rivosinc.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>