msm: drm: dp: register SDE power client for Display Port driver

Register Display Port as a client to the SDE power handler driver.
This is needed to enable/disable the SDE core clocks whenever needed
during Display Port enable/disable sequence. Remove the SDE core clocks
from Display Port dtsi node for SDM845 since the SDE power handler
takes care of controlling these clocks now.

Change-Id: I2c9c608b186936a427b1071b321e4188e01450aa
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>