Create a new SPARC32_DMA container object (including an appropriate container
memory region) and add instances of the SPARC32_ESPDMA_DEVICE and
SPARC32_LEDMA_DEVICE as child objects. The benefit is that most of the gpio
wiring complexity between esp/espdma and lance/ledma is now hidden within the
SPARC32_DMA realize function.

Since the sun4m IOMMU is already QOMified we can find a reference to
it using object_resolve_path_type() allowing us to completely remove all external
references to the iommu pointer.

Finally we rework sun4m's sparc32_dma_init() to invoke the new SPARC32_DMA object
and wire up the remaining board memory regions/IRQs.
Signed-off-by: NMark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: NArtyom Tarasenko <atar4qemu@gmail.com>
Acked-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>