net: dpaa2: improve PTP Kconfig option

Converted to use "imply" instead of "select" for PTP_1588_CLOCK
driver selecting. This could break the hard dependency between
the PTP clock subsystem and ethernet drivers.
This patch also set "default y" for dpaa2 ptp driver building to
provide user an available ptp clock in default.
Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/dpaa2/Kconfig

@@ -9,8 +9,9 @@ config FSL_DPAA2_ETH
 
 config FSL_DPAA2_PTP_CLOCK
 	tristate "Freescale DPAA2 PTP Clock"
-	depends on FSL_DPAA2_ETH && POSIX_TIMERS
-	select PTP_1588_CLOCK
+	depends on FSL_DPAA2_ETH
+	imply PTP_1588_CLOCK
+	default y
 	help
 	  This driver adds support for using the DPAA2 1588 timer module
 	  as a PTP clock.