msm: ADSPRPC: Add channel for compute/modem DSP

Add new channel to allow for communication to be established
between application and compute/modem DSP to enable RPC calls to
be made.

Change-Id: I98e443e894d81bcd815418f2a79723db14d87ce4
Signed-off-by: Sathish Ambley <sathishambley@codeaurora.org>