powerpc: dts: p2020: Add ptp_clock@24e00 node via pq3-etsec1-timer-0.dtsi

Import pq3-etsec1-timer-0.dtsi device tree include file from upstream Linux
kernel for P2020. This allows U-Boot to use P2020 device tree files from
upstream Linux kernel which reference ptp_clock@24e00 device.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>