drm/msm/dp: fix voltage and pre-emphasis values

Correct the Voltage swing and pre-emphasis values for DisplayPort
PHY as per hardware recommendations.

CRs-Fixed: 2220185
Change-Id: I8bcd4630b7a5a33f76c941018fc4c5e814c73047
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>