arm64: dts: imx8mp-venice-gw73xx: add mac addr for eth1

arm64: dts: imx8mp-venice-gw73xx: add mac addr for eth1

The SoM used on this board does not bring down the pins for the QOS
ethernet and instead offers the 2nd ethernet as a PCI GbE device.

Set the alias as such and add the PCI bus topology for eth1 so that
boot firmware can set the local-mac-address property.

The eth1 device is behind a PCI switch:
 # lspci -n
 00:00.0 0604: 16c3:abcd (rev 01)
 01:00.0 0604: 12d8:2608
 02:01.0 0604: 12d8:2608
 02:02.0 0604: 12d8:2608
 02:03.0 0604: 12d8:2608
 02:04.0 0604: 12d8:2608
 c0:00.0 0200: 1055:7430 (rev 11)
 # lspci -t
 -[0000:00]---00.0-[01-ff]----00.0-[02-fe]--+-01.0-[03-41]--
                                           +-02.0-[42-80]--
                                           +-03.0-[81-bf]--
                                           \-04.0-[c0-fe]----00.0

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>