arm64: defconfig: Change CONFIG_AT803X_PHY from m to y

With phy-reset-gpios are enabled for i.MX8MM-EVK board, phy
will be reset. Without CONFIG_AT803X_PHY as y, board will stop
booting in NFS DHCP, because phy is not ready. So mark
CONFIG_AT803X_PHY from m to y to make board boot when using nfs rootfs.
Signed-off-by: NPeng Fan <peng.fan@nxp.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>

arch/arm64/configs/defconfig

@@ -286,7 +286,7 @@ CONFIG_SNI_AVE=y
 CONFIG_SNI_NETSEC=y
 CONFIG_STMMAC_ETH=m
 CONFIG_MDIO_BUS_MUX_MMIOREG=y
-CONFIG_AT803X_PHY=m
+CONFIG_AT803X_PHY=y
 CONFIG_MARVELL_PHY=m
 CONFIG_MARVELL_10G_PHY=m
 CONFIG_MESON_GXL_PHY=m