If CONFIG_PTP_1588_CLOCK=m and CONFIG_SFC_SIENA=y, the siena driver will fail to link:

drivers/net/ethernet/sfc/siena/ptp.o: In function `efx_ptp_remove_channel':
ptp.c:(.text+0xa28): undefined reference to `ptp_clock_unregister'
drivers/net/ethernet/sfc/siena/ptp.o: In function `efx_ptp_probe_channel':
ptp.c:(.text+0x13a0): undefined reference to `ptp_clock_register'
ptp.c:(.text+0x1470): undefined reference to `ptp_clock_unregister'
drivers/net/ethernet/sfc/siena/ptp.o: In function `efx_ptp_pps_worker':
ptp.c:(.text+0x1d29): undefined reference to `ptp_clock_event'
drivers/net/ethernet/sfc/siena/ptp.o: In function `efx_siena_ptp_get_ts_info':
ptp.c:(.text+0x301b): undefined reference to `ptp_clock_index'

To fix this build error, make SFC_SIENA depends on PTP_1588_CLOCK.
Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: d48523cb ("sfc: Copy shared files needed for Siena (part 2)")
Signed-off-by: Ren Zhijie <renzhijie2@huawei.com>
Acked-by: Martin Habets <habetsm.xilinx@gmail.com>
Link: https://lore.kernel.org/r/20220513012721.140871-1-renzhijie2@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>