soc: qcom: bam_dmux: Cache callback information

Callback notifications lock the channel status to prevent clients from
unregistering their callback function and other information while it is
in use during a notification.  However, in some scenarios, clients use
the notification context to call back into bam_dmux which can result in
lock recursion.

Avoid the issue by caching the callback information, and then unlocking
the channel state before invoking the client's callback.

CRs-Fixed: 690328
Change-Id: I764b1c21c2254c9c72ee329dc671f9a1afb648a2
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>