ARM: dts: msm: enable DP support on SA6155 & SA6155P

Add DP and DP MST registers and regulators for
SA6155 & SA6155P based ADP Star platform to support
DP & DP MST display.

Change-Id: Ic759aa47e3d06cb3a413e0b124bd9ee262da56a7
Signed-off-by: Rahul Sharma <rahsha@codeaurora.org>