arm64: defconfig: remove CONFIG_USB_QCOM_8X16_PHY

No Qualcomm SoC requires the "phy-qcom-8x16-usb.c" USB phy driver
support any more.  Remove the code, and remove the config option
from the arm64 defconfig.

Suggested-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Andy Gross <andy.gross@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>