msm: ADSPRPC: Enable RPC on SLPI processor

Add new channel to be able to communicate with SLPI processor
and do remote procedure calls from Apps subsystem. The Apps
and SLPI subsystems would use the memory from ADSP ION heap
for sharing the input and output buffers.

Change-Id: I186ec8e7769011d7aeeba149017f1555f2d84ed7
Signed-off-by: Sathish Ambley <sathishambley@codeaurora.org>