hw/core/sysbus: Introduce sysbus_mmio_map_name() helper

hw/core/sysbus: Introduce sysbus_mmio_map_name() helper

Some sysbus devices have conditional mmio regions. This
happens for instance with the hw/acpi/ged device. In that case
it becomes difficult to predict which index a specific MMIO
region corresponds to when one needs to mmio map the region.
Introduce a new helper that takes the name of the region instead
of its index. If the region is not found this returns -1.
Otherwise it maps the corresponding index and returns this latter.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20250714080639.2525563-31-eric.auger@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>