dt-bindings: mhi: net_dev: update devicetree doc for supporting rsc device

RSC channel operates in conjunction with IP_HW0 device. Updating
devicetree documentation instruction to show linking of the
two devices together.

CRs-Fixed: 2361266
Change-Id: I99ccea29fcfdea7ab1d9cb792c4e8bd0e2f5f727
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>