hw/riscv/riscv-iommu: add Address Translation Cache (IOATC)

The RISC-V IOMMU spec predicts that the IOMMU can use translation caches
to hold entries from the DDT. This includes implementation for all cache
commands that are marked as 'not implemented'.

There are some artifacts included in the cache that predicts s-stage and
g-stage elements, although we don't support it yet. We'll introduce them
next.

Signed-off-by: Tomasz Jeznach <tjeznach@rivosinc.com>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20241016204038.649340-9-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

hw/riscv/riscv-iommu.h

@@ -69,6 +69,9 @@ struct RISCVIOMMUState {
 
     GHashTable *ctx_cache;          /* Device translation Context Cache */
 
+    GHashTable *iot_cache;          /* IO Translated Address Cache */
+    unsigned iot_limit;             /* IO Translation Cache size limit */
+
     /* MMIO Hardware Interface */
     MemoryRegion regs_mr;
     uint8_t *regs_rw;  /* register state (user write) */