ARM: dts: msm: add 7nm dp phy pll node on SDM855

Patch sets mdss_dp_pll node as compatible with
"qcom,mdss_dp_pll_7nm" module and adds "gcc_iface"
clock as a dependency on SDM855.

Change-Id: Ia5a949a9a3eaee92f0cfe4e132de31f70becec2c
Signed-off-by: Alexander Beykun <abeykun@codeaurora.org>