arm: dts: lx2160a: add label to pcie nodes in dts

Add label to pcie nodes in dts so that these nodes
are easy to refer.

Signed-off-by: Wasim Khan <wasim.khan@nxp.com>
[Rebased]
Signed-off-by: Priyanka Jain <priyanka.jain@nxp.com>