arm: dts: qcom: apq8064: Add display DT nodes

APQ8064 contains a MDP4 based display controller. It contains a HDMI, LVDS
and 2 DSI outputs.

Add display DT nodes for MDP4, HDMI TX and HDMI PHY. MDP4 based display
blocks have a flat device hierarchy.

Nodes for other outputs will be added later.

Cc: devicetree@vger.kernel.org

Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>