dt-bindings: msm/dsi: Some binding doc cleanups

Some cleanups:

- Use simpler names for DT nodes in the example
- Use references instead of dumping Document links everywhere

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>