ptp: Make PTP_1588_CLOCK select rather than depend on PPS

PTP hardware clock drivers that select PTP_1588_CLOCK must currently
also select PPS.  For those drivers that don't, the user must enable
PPS, then enable PTP_1588_CLOCK, then the driver.  Simplify things for
developers and users by putting this selection in one place.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/ptp/Kconfig b/drivers/ptp/Kconfig
index a6e4b7c..131ef03 100644
--- a/drivers/ptp/Kconfig
+++ b/drivers/ptp/Kconfig
@@ -4,12 +4,9 @@
 
 menu "PTP clock support"
 
-comment "Enable Device Drivers -> PPS to see the PTP clock options."
-	depends on PPS=n
-
 config PTP_1588_CLOCK
 	tristate "PTP clock support"
-	depends on PPS
+	select PPS
 	help
 	  The IEEE 1588 standard defines a method to precisely
 	  synchronize distributed clocks over Ethernet networks. The