igc: fix build errors for PTP

When IGC=y and PTP_1588_CLOCK=m, the ptp_*() interface family is
not available to the igc driver. Make this driver depend on
PTP_1588_CLOCK_OPTIONAL so that it will build without errors.

Various igc commits have used ptp_*() functions without checking
that PTP_1588_CLOCK is enabled. Fix all of these here.

Fixes these build errors:

ld: drivers/net/ethernet/intel/igc/igc_main.o: in function `igc_msix_other':
igc_main.c:(.text+0x6494): undefined reference to `ptp_clock_event'
ld: igc_main.c:(.text+0x64ef): undefined reference to `ptp_clock_event'
ld: igc_main.c:(.text+0x6559): undefined reference to `ptp_clock_event'
ld: drivers/net/ethernet/intel/igc/igc_ethtool.o: in function `igc_ethtool_get_ts_info':
igc_ethtool.c:(.text+0xc7a): undefined reference to `ptp_clock_index'
ld: drivers/net/ethernet/intel/igc/igc_ptp.o: in function `igc_ptp_feature_enable_i225':
igc_ptp.c:(.text+0x330): undefined reference to `ptp_find_pin'
ld: igc_ptp.c:(.text+0x36f): undefined reference to `ptp_find_pin'
ld: drivers/net/ethernet/intel/igc/igc_ptp.o: in function `igc_ptp_init':
igc_ptp.c:(.text+0x11cd): undefined reference to `ptp_clock_register'
ld: drivers/net/ethernet/intel/igc/igc_ptp.o: in function `igc_ptp_stop':
igc_ptp.c:(.text+0x12dd): undefined reference to `ptp_clock_unregister'
ld: drivers/platform/x86/dell/dell-wmi-privacy.o: in function `dell_privacy_wmi_probe':

Fixes: 64433e5 ("igc: Enable internal i225 PPS")
Fixes: 60dbede ("igc: Add support for ethtool GET_TS_INFO command")
Fixes: 8793885 ("igc: enable auxiliary PHC functions for the i225")
Fixes: 5f29580 ("igc: Add basic skeleton for PTP")
Signed-off-by: Randy Dunlap <[email protected]>
Cc: Ederson de Souza <[email protected]>
Cc: Tony Nguyen <[email protected]>
Cc: Vinicius Costa Gomes <[email protected]>
Cc: Jeff Kirsher <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Jesse Brandeburg <[email protected]>
Cc: [email protected]
Acked-by: Vinicius Costa Gomes <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

drivers/net/ethernet/intel/Kconfig

@@ -335,6 +335,7 @@ config IGC
 	tristate "Intel(R) Ethernet Controller I225-LM/I225-V support"
 	default n
 	depends on PCI
+	depends on PTP_1588_CLOCK_OPTIONAL
 	help
 	  This driver supports Intel(R) Ethernet Controller I225-LM/I225-V
 	  family of adapters.