mach-snapdragon: fixup USB nodes

mach-snapdragon: fixup USB nodes

We don't support USB super-speed in U-Boot yet, we lack the SS PHY
drivers, however from my testing even with a PHY driver there seem to be
other issues when talking to super-speed peripherals.

In pursuit of maintaining upstream DT compatibility, and simplifying
porting for new devices, let's implement the DT fixups necessary to
configure USB in high-speed only mode at runtime. The pattern is
identical for all Qualcomm boards that use the Synaptics DWC3
controller:

* Add an additional property on the Qualcomm wrapper node
* Remove the super-speed phy phandle and phy-name entries.

Acked-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>