ARM: dts: msm: Add cdsp rpmsg entry in Lahaina

CDSPRM module relies on the rpmsg node to create a communication
channel with CDSP. The node also carries information for Cx i-peak
limit management, CPU QoS voting, HVX, CDSP thermal mitigation
frameworks.
CDSPRM module implements a RPMSG interface to communicate with CDSP
while providing a way for CDSP to vote for CPU L3 clock, CPU QoS to
benefit CDSP applications performance. The module also implements
an interface with NPU for Cx i-peak limit management and registers
cooling devices for CDSP and HVX thermal mitigation.
Documentation for device tree bindings related to CDSPRM.

Change-Id: I0f79ebcfcd2e6a2366f755278ae2c5f6bc1b8199