dt-bindings: phy: qcom,qmp-usb3-dp: Add DP phy information

This binding only describes the USB phy inside the USB3 + DP "combo"
phy. Add information for the DP phy and describe the sub-nodes that
represent the DP and USB3 phys that exist inside the combo wrapper.
Remove reg-names from required properties because it isn't required nor
used by the kernel driver.

Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Jeykumar Sankaran <jsanka@codeaurora.org>
Cc: Chandan Uddaraju <chandanu@codeaurora.org>
Cc: Vara Reddy <varar@codeaurora.org>
Cc: Tanmay Shah <tanmay@codeaurora.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Manu Gautam <mgautam@codeaurora.org>
Cc: Sandeep Maheswaram <sanm@codeaurora.org>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Jonathan Marek <jonathan@marek.ca>
Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: <devicetree@vger.kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Rob Clark <robdclark@chromium.org>
Link: https://lore.kernel.org/r/20200916231202.3637932-2-swboyd@chromium.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>