net: broadcom: Fix BCMGENET Kconfig

While BCMGENET select BROADCOM_PHY as y, but PTP_1588_CLOCK_OPTIONAL is m,
kconfig warning and build errors:

WARNING: unmet direct dependencies detected for BROADCOM_PHY
  Depends on [m]: NETDEVICES [=y] && PHYLIB [=y] && PTP_1588_CLOCK_OPTIONAL [=m]
  Selected by [y]:
  - BCMGENET [=y] && NETDEVICES [=y] && ETHERNET [=y] && NET_VENDOR_BROADCOM [=y] && HAS_IOMEM [=y] && ARCH_BCM2835 [=y]

drivers/net/phy/broadcom.o: In function `bcm54xx_suspend':
broadcom.c:(.text+0x6ac): undefined reference to `bcm_ptp_stop'
drivers/net/phy/broadcom.o: In function `bcm54xx_phy_probe':
broadcom.c:(.text+0x784): undefined reference to `bcm_ptp_probe'
drivers/net/phy/broadcom.o: In function `bcm54xx_config_init':
broadcom.c:(.text+0xd4c): undefined reference to `bcm_ptp_config_init'

Fixes: 99addbe3 ("net: broadcom: Select BROADCOM_PHY for BCMGENET")
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Acked-by: NFlorian Fainelli <f.fainelli@broadcom.com>
Link: https://lore.kernel.org/r/20221105090245.8508-1-yuehaibing@huawei.comSigned-off-by: NJakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/broadcom/Kconfig

@@ -77,7 +77,7 @@ config BCMGENET
 	select BCM7XXX_PHY
 	select MDIO_BCM_UNIMAC
 	select DIMLIB
-	select BROADCOM_PHY if ARCH_BCM2835
+	select BROADCOM_PHY if (ARCH_BCM2835 && PTP_1588_CLOCK_OPTIONAL)
 	help
 	  This driver supports the built-in Ethernet MACs found in the
 	  Broadcom BCM7xxx Set Top Box family chipset.