cnss2: Use separate DT entry to add firmware path prefix

qcom,converged-dt is meant to use one DT node which has multiple
sub-nodes to support multiple devices. There is also one simple
scenario that one same DT node can be directly used by multiple
devices without creating sub-nodes. Use separate DT entry for such
case to add firmware path prefix to simplify implementation and
avoid conflicts.

Change-Id: I3beb3dfce30d31f086eeb6667afa83560880ff32
Signed-off-by: Yue Ma <yuem@codeaurora.org>