arm64: dts: fsl: add ptp timer node for dpaa2 platforms

This patch is to add ptp timer device tree node for dpaa2
platforms(ls1088a/ls208xa/lx2160a).

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>