enetc: Select PHYLIB while CONFIG_FSL_ENETC_VF is set

Like FSL_ENETC, when CONFIG_FSL_ENETC_VF is set,
we should select PHYLIB, otherwise building still fails:

drivers/net/ethernet/freescale/enetc/enetc.o: In function `enetc_open':
enetc.c:(.text+0x2744): undefined reference to `phy_start'
enetc.c:(.text+0x282c): undefined reference to `phy_disconnect'
drivers/net/ethernet/freescale/enetc/enetc.o: In function `enetc_close':
enetc.c:(.text+0x28f8): undefined reference to `phy_stop'
enetc.c:(.text+0x2904): undefined reference to `phy_disconnect'
drivers/net/ethernet/freescale/enetc/enetc_ethtool.o:(.rodata+0x3f8): undefined reference to `phy_ethtool_get_link_ksettings'
drivers/net/ethernet/freescale/enetc/enetc_ethtool.o:(.rodata+0x400): undefined reference to `phy_ethtool_set_link_ksettings'

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: d4fd0404 ("enetc: Introduce basic PF and VF ENETC ethernet drivers")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>