cpsw/netcp: refine cpts dependency

Tony Lindgren reports a kernel oops that resulted from my compile-time
fix on the default config. This shows two problems:

a) configurations that did not already enable PTP_1588_CLOCK will
   now miss the cpts driver

b) when cpts support is disabled, the driver crashes. This is a
   preexisting problem that we did not notice before my patch.

While the second problem is still being investigated, this modifies
the dependencies again, getting us back to the original state, with
another 'select NET_PTP_CLASSIFY' added in to avoid the original
link error we got, and the 'depends on POSIX_TIMERS' to hide
the CPTS support when turning it on would be useless.

Cc: stable@vger.kernel.org # 4.11 needs this
Fixes: 07fef362 ("cpsw/netcp: cpts depends on posix_timers")
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Tested-by: NTony Lindgren <tony@atomide.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/Kconfig

@@ -76,7 +76,7 @@ config TI_CPSW
 config TI_CPTS
 	bool "TI Common Platform Time Sync (CPTS) Support"
 	depends on TI_CPSW || TI_KEYSTONE_NETCP
-	depends on PTP_1588_CLOCK
+	depends on POSIX_TIMERS
 	---help---
 	  This driver supports the Common Platform Time Sync unit of
 	  the CPSW Ethernet Switch and Keystone 2 1g/10g Switch Subsystem.
@@ -87,6 +87,8 @@ config TI_CPTS_MOD
 	tristate
 	depends on TI_CPTS
 	default y if TI_CPSW=y || TI_KEYSTONE_NETCP=y
+	select NET_PTP_CLASSIFY
+	imply PTP_1588_CLOCK
 	default m
 
 config TI_KEYSTONE_NETCP