hw/net/allwinner-sun8i-emac: Use AddressSpace for DMA transfers

hw/net/allwinner-sun8i-emac: Use AddressSpace for DMA transfers

Allow the device to execute the DMA transfers in a different
AddressSpace.

The H3 SoC keeps using the system_memory address space,
but via the proper dma_memory_access() API.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Tested-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Message-id: 20200814122907.27732-1-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>