ARM: dts: msm: Add USB GDSC reference to apq8084

USB 3.0 controller needs to control its GDSC supply in
order to gate on/off for operation.

Change-Id: Idb46af072f4bfbe92e980ef20e85e8d4915a4b72
Signed-off-by: Jack Pham <jackp@codeaurora.org>