ARM: dts: msm8974-FP2: Add USB node

This introduces the usb node which can be used e.g. for USB_ETH

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>