powerpc/83xx: gianfar_ptp: select 1588 clock source through dts file

Currently IEEE 1588 timer reference clock source is determined through
hard-coded value in gianfar_ptp driver. This patch allows to select ptp
clock source by means of device tree file node.

For instance:

	fsl,cksel = <0>;

for using external (TSEC_TMR_CLK input) high precision timer
reference clock.

Other acceptable values:

	<1> : eTSEC system clock
	<2> : eTSEC1 transmit clock
	<3> : RTC clock input

When this attribute isn't used, eTSEC system clock will serve as
IEEE 1588 timer reference clock.

Signed-off-by: Aida Mynzhasova <aida.mynzhasova@skitlab.ru>
Acked-by: Kumar Gala <galak@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/freescale/gianfar_ptp.c b/drivers/net/ethernet/freescale/gianfar_ptp.c
index 098f133..e006a09 100644
--- a/drivers/net/ethernet/freescale/gianfar_ptp.c
+++ b/drivers/net/ethernet/freescale/gianfar_ptp.c
@@ -452,7 +452,9 @@
 	err = -ENODEV;
 
 	etsects->caps = ptp_gianfar_caps;
-	etsects->cksel = DEFAULT_CKSEL;
+
+	if (get_of_u32(node, "fsl,cksel", &etsects->cksel))
+		etsects->cksel = DEFAULT_CKSEL;
 
 	if (get_of_u32(node, "fsl,tclk-period", &etsects->tclk_period) ||
 	    get_of_u32(node, "fsl,tmr-prsc", &etsects->tmr_prsc) ||