arm64: dts: qcom: sc7180: Add Display Port dt node

Add DP device node on sc7180.

Changes in v2:

- Add assigned-clocks and assigned-clock-parents
- Remove cell-index and pixel_rcg
- Change compatible to qcom,sc7180-dp

Changes in v3:
- Update commit text
- Make DP child node of MDSS
- Remove data-lanes property from SOC dts
- Disable DP node in SOC dts
- Assign DP to Port2 in MDP node
- Add MDSS AHB clock in DP device node

Changes in v4:
- Remove redundant reg-names property
- Use IRQ flag instead had hard coded value.
- Add link clock source in assigned-clocks list.

Changes in v5:
- Add OPP table and power-domains for DisplayPort

Changes in v6:
- Remove redundant IRQ flag

Signed-off-by: Tanmay Shah <tanmay@codeaurora.org>
Co-developed-by: Kuogee Hsieh <khsieh@codeaurora.org>
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>