soc:qcom:spcom: multi clients support

This change enables for more than one client to communicate to SP server
simultaneously. The feature is configured by the userspace during channel
creation. Per channel mutex is used to implement the atomicity of single
client request/respose excgange.

Change-Id: I3670fcdad26cc8879f57ebe32c07a93d69560779
Signed-off-by: Konstantin Dorfman <kdorfman@codeaurora.org>
Signed-off-by: Li(Lily) Li <liil@codeaurora.org>