ACPI: RISC-V: Add support for RIMT

RISC-V IO Mapping Table (RIMT) is a static ACPI table to communicate
IOMMU information to the OS. The spec is available at [1].

The changes at high level are,
	a) Initialize data structures required for IOMMU/device
	   configuration using the data from RIMT. Provide APIs required
	   for device configuration.
	b) Provide an API for IOMMU drivers to register the
	   fwnode with RIMT data structures. This API will create a
	   fwnode for PCIe IOMMU.

[1] - https://github.com/riscv-non-isa/riscv-acpi-rimt

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20250818045807.763922-2-sunilvl@ventanamicro.com
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

arch/riscv/Kconfig

@@ -16,6 +16,7 @@ config RISCV
 	select ACPI_MCFG if (ACPI && PCI)
 	select ACPI_PPTT if ACPI
 	select ACPI_REDUCED_HARDWARE_ONLY if ACPI
+	select ACPI_RIMT if ACPI
 	select ACPI_SPCR_TABLE if ACPI
 	select ARCH_DMA_DEFAULT_COHERENT
 	select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION