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

CDSPRM module relies on the irpmsg node to create a communication
channel with CDSP. The node also carries information for Cx i-peak
limit management, CPU QoS voting.
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.

Change-Id: I7bdc9d2961edff0bacd010d16f5cd6de06c25537