arm64: dts: lx2160a: describe the SerDes block #2

Add description for the LX2160A second SerDes block.
It is functionally identical to the first one already added in
commit 3cbe93a1 ("arch: arm64: dts: lx2160a: describe the SerDes
block #1").

The SerDes driver currently updates the registers of all 8 lanes by
default during probe. Because currently this driver only supports
configuration of network protocols, this can lead to problems with
certain configurations.
Set status property to "disabled" by default so that existing boards are
not impacted.

Signed-off-by: Josua Mayer <josua@solid-run.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>