selftests/tc-testing: add ptp_mock Kconfig dependency

For offloaded tc-taprio testing with netdevsim, the mock-up PHC driver
is used.
Suggested-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20230807193324.4128292-10-vladimir.oltean@nxp.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/tc-testing/config

@@ -96,10 +96,11 @@ CONFIG_NET_SCH_FIFO=y
 CONFIG_NET_SCH_ETS=m
 CONFIG_NET_SCH_RED=m
 CONFIG_NET_SCH_FQ_PIE=m
-CONFIG_NETDEVSIM=m
 
 #
 ## Network testing
 #
 CONFIG_CAN=m
 CONFIG_ATM=y
+CONFIG_NETDEVSIM=m
+CONFIG_PTP_1588_CLOCK_MOCK=m