arm64: dts: qcom: msm8996: add second DSI interface

Add device nodes for the DSI1, second DSI interface found on
MSM8996/APQ8096 platforms. For example on db820c it is routed to the
secondary HS expansion connector.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220617103652.606250-1-dmitry.baryshkov@linaro.org