drm/msm/dp: Fix for CTS link training failures on sm6150

Link training failures are observed in CTS on changing lane
count. The updated lane count is not getting programmed before
the link training. So, adding changes to program the lane count
before the start of link training sequence.

Change-Id: I133c282fd42a232753a39456598090b6c87c0065
Signed-off-by: Sankeerth Billakanti <sbillaka@codeaurora.org>