hw/riscv/riscv-iommu: add IOHPMCYCLES mmio write

hw/riscv/riscv-iommu: add IOHPMCYCLES mmio write

RISCV_IOMMU_REG_IOHPMCYCLES writes are done by
riscv_iommu_process_hpmcycle_write(), called by the mmio write callback
via riscv_iommu_process_hpm_writes().

Signed-off-by: Tomasz Jeznach <tjeznach@rivosinc.com>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250224190826.1858473-8-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>