hw/arm/allwinner-h3: add EMAC ethernet device

hw/arm/allwinner-h3: add EMAC ethernet device

The Allwinner Sun8i System on Chip family includes an Ethernet MAC (EMAC)
which provides 10M/100M/1000M Ethernet connectivity. This commit
adds support for the Allwinner EMAC from the Sun8i family (H2+, H3, A33, etc),
including emulation for the following functionality:

 * DMA transfers
 * MII interface
 * Transmit CRC calculation

Signed-off-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20200311221854.30370-10-nieklinnenbank@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>