hw/riscv/riscv-iommu: add riscv-iommu-hpm file

hw/riscv/riscv-iommu: add riscv-iommu-hpm file

The HPM (Hardware Performance Monitor) support consists of almost 7
hundred lines that would be put on top of the base riscv-iommu
emulation.

To avoid clogging riscv-iommu.c, add a separated riscv-iommu-hpm file
that will contain HPM specific code.

We'll start by adding riscv_iommu_hpmcycle_read(), a helper that will be
called during the riscv_iommu_mmio_read() callback.

This change will have no effect on the existing emulation since we're
not declaring HPM feature support.

Signed-off-by: Tomasz Jeznach <tjeznach@rivosinc.com>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250224190826.1858473-4-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>