video: msm: mdss: mdss_dsi_panel_driver: Add somc,no-vsp-gpio property

Some devices don't need/have this GPIO, so the driver
can continue to go through its code even if we
haven't specified the somc,vsp-gpio property.
arm: Eagle: Welcome to the Sony Unified display driver
Merge pull request #47 from kholk/aosp/LNX.LA.3.5.1-03010-8x74.0

Aosp/lnx.la.3.5.1 03010 8x74.0