hw/i386/intel_iommu: Do not use SysBus API to map local MMIO region

There is no point in exposing an internal MMIO region via
SysBus and directly mapping it in the very same device.

Just map it without using the SysBus API.

Transformation done using the following coccinelle script:

  @@
  expression sbdev;
  expression index;
  expression addr;
  expression subregion;
  @@
  -    sysbus_init_mmio(sbdev, subregion);
       ... when != sbdev
  -    sysbus_mmio_map(sbdev, index, addr);
  +    memory_region_add_subregion(get_system_memory(), addr, subregion);

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Message-Id: <20231018141151.87466-3-philmd@linaro.org>