ARM: dts: msm: Model usb3 pipe clk as gate clock

Due to usb pipe clock tree limitation, the parent clock
can not be turned off after the branch clock. Therefore,
model the gcc_usb3_pipe_clk as gate clock to avoid the
check of the status bit change for this branch clock.

Change-Id: I343a3582532743f9876a78c8fdd83c05b82a901a
Signed-off-by: Tianyi Gou <tgou@codeaurora.org>