net: wangxun: fix LIBWX dependencies

net: wangxun: fix LIBWX dependencies

Selecting LIBWX requires that its dependencies are met first:

WARNING: unmet direct dependencies detected for LIBWX
  Depends on [m]: NETDEVICES [=y] && ETHERNET [=y] && NET_VENDOR_WANGXUN [=y] && PTP_1588_CLOCK_OPTIONAL [=m]
  Selected by [y]:
  - TXGBE [=y] && NETDEVICES [=y] && ETHERNET [=y] && NET_VENDOR_WANGXUN [=y] && PCI [=y] && COMMON_CLK [=y] && I2C_DESIGNWARE_PLATFORM [=y]
ld.lld-21: error: undefined symbol: ptp_schedule_worker
>>> referenced by wx_ptp.c:747 (/home/arnd/arm-soc/drivers/net/ethernet/wangxun/libwx/wx_ptp.c:747)
>>>               drivers/net/ethernet/wangxun/libwx/wx_ptp.o:(wx_ptp_reset) in archive vmlinux.a

Add the smae dependency on PTP_1588_CLOCK_OPTIONAL to the two driver
using this library module.

Fixes: 06e75161b9d4 ("net: wangxun: Add support for PTP clock")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://patch.msgid.link/20250224140516.1168214-1-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>