drivers: dsa_nxp_imx_netc: improve PTP timestamping enablement PTP timestamping should be enabled only when NET_L2_PTP and PTP_CLOCK_NXP_NETC are selected. And NET_PKT_CONTROL_BLOCK is required for PTP timestamping code. Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>