dt-bindings: display: msm: document DSI controller and phy on SA8775P

Document DSI controller and phy on SA8775P platform.

Signed-off-by: Ayushi Makhija <quic_amakhija@quicinc.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/649839/
Link: https://lore.kernel.org/r/20250424062431.2040692-4-quic_amakhija@quicinc.com


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>