msm: mdss: displayport: fix alt mode pin configurations

Correct the pin configuration selection logic during alt mode.
Also, fix the message to be sent to usb to avoid sink or dongle
reporting error or nack.

Change-Id: I6c6f9e0c9738af4766a7ff8acb3c932be55935de
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>