disp: msm: dp: disable ASSR before link training

Power on reset value of DPTX_CONFIGURATION_CTRL.ASSR (alternate scrambler
seed reset) is high. This fails link training 2 with TPS4 pattern.
Change disables this before link training starts.

Change-Id: Iee95de04625658254b242afdcbba6db24a52606d
Signed-off-by: Vara Reddy <varar@codeaurora.org>
Signed-off-by: Navjyot SINGH <quic_navjsing@quicinc.com>