dt-bindings: phy: qcom-qusb2: Add support for overriding Phy tuning parameters

Add support for overriding QUSB2 V2 phy tuning parameters
in device tree bindings.

Signed-off-by: Sandeep Maheswaram <sanm@codeaurora.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>