ARM: dts: msm: add the dtsi entries for DP PLL clocks for msm8998

The parent of DP VCO divided mux clock needs to be set from the
Display Port driver based on the link rate. Add the dtsi entries
needs for this support for msm8998.

Change-Id: I76c2568579735f20106e40a359fd0052a2f51fbf
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>