msm: ADSPRPC: Save and restore contexts when interrupted

While a RPC session is in progress, wait could get interrupted
as a result of device entering power collase and the system call
retried once the device leaves power collapse. This requires that
the RPC session context is saved and restored across these
interrupts to avoid duplicate invocations being sent across to
the remote processor.

Change-Id: I71141c13da7be3d33e13305e0744148921123160
Acked-by: Sathish Ambley <sambley@qti.qualcomm.com>
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>