ipq806x: automatically select kmod-usb-phy-qcom-dwc3

kmod-usb-phy-qcom-dwc3 is required to get USB working on ipq806x. It was
missed in previous commit so let's enable it automatically.

Signed-off-by: Mathieu Olivari <mathieu@codeaurora.org>

SVN-Revision: 45345