MAINTAINERS: update files maintained under DPAA2 PTP/ETHERNET

The files maintained under DPAA2 PTP/ETHERNET needs to
be updated since dpaa2 ptp driver had been moved into
drivers/net/ethernet/freescale/dpaa2/.

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