ARM: dts: msm: add dsi secondary node for SM8150

Add secondary DSI node to device tree. This enables
display sub-system to support multiple DSI displays.

CRs-Fixed: 2254681
Change-Id: I8674c2fc3862f7641f1eafe3b111c9a7bafcb787
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>