hw/net:ftgmac100: update ring base address to 64 bits

hw/net:ftgmac100: update ring base address to 64 bits

Update TX and RX ring base address data type to uint64_t for
64 bits dram address DMA support.

Both "Normal Priority Transmit Ring Base Address Register(0x20)" and
"Receive Ring Base Address Register (0x24)" are used for saving the
low part physical address of descriptor manager.

Therefore, changes to set TX and RX descriptor manager address bits [31:0]
in ftgmac100_read and ftgmac100_write functions.

Incrementing the version of vmstate to 2.

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>