arm64: mvebu: armada-7040-db.dts: Change eth1 speed from 2.5G to 1G

arm64: mvebu: armada-7040-db.dts: Change eth1 speed from 2.5G to 1G

The default configuration for the COMPHY-0 port should be 1G, as its
used as 1G SGMII connection. This change is necessary to get the
MAC2 port (SGMII) working on this DB.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Stefan Chulski <stefanc@marvell.com>
Cc: Kostya Porotchkin <kostap@marvell.com>
Cc: Nadav Haklai <nadavh@marvell.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>