arm64: dts: qcom: sc8180x: modernize MDSS device definition

arm64: dts: qcom: sc8180x: modernize MDSS device definition

Follow the lead of other platforms and update DT description of the MDSS
device:

- Use generic node names (dislpay-subsystem, display-controller, phy)
  instead of the platform-specific ones (mdss, mdp, dsi-phy)
- Add platform-specific compatible string to DSI controllers.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250704-mdss-schema-v1-4-e978e4e73e14@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>