drm/msm/dp: skip gpio driving in simulation mode

On sm6150, the DP driver is driving the lane switch
mux through gpio to toggle super-speed lanes for
usb or DP use based on DP connect event. In
simulation mode, the mux is toggling the super-speed
lanes to DP after connect command is issued through
the debugfs node. This is causing a loss of usb
connection leading to communication cutoff between
the simulation runtime environemnt and the device.
These changes will skip gpio toglging during the
simulation mode to avoid the usb connection loss.

Change-Id: I8dd2a4f0af8451e3037d8c03c75ac711818cd217
Signed-off-by: Sankeerth Billakanti <sbillaka@codeaurora.org>