arm64: defconfig: enable the SerDes PHY for Qualcomm DWMAC

Enable the SGMII/SerDes PHY driver. This module is required to enable
ethernet on Qualcomm sa8775p platforms.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230622121141.218623-1-brgl@bgdev.pl


Signed-off-by: Bjorn Andersson <andersson@kernel.org>