ARM: dts: msm: add MSM External display node for msmcobalt

Add MSM External display node for msmcobalt which is needed
to manage the interaction between external displays (HDMI and
Display Port) and the audio and display frameworks.

CRs-Fixed: 1009284
Change-Id: I54c1eee7a3e1d8f481a9bc629e28f13c5849a3db
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>