remoteproc: omap: differentiate auto-suspend from system suspend

The omap remoteproc driver sends a mailbox message to the remote
processor requesting it to save its context and then be suspended.
This can happen either through the runtime auto-suspend path or
through the system suspend.

The mailbox message being sent to the remote processor is now
differentiated between the two paths. This differentiation provides
flexibility on the remote processor to allow an application cancel
auto-suspend. This flexibility is needed as there can be some
operations wherein there is no on-going activity between the host
and the remote processor with the remote processor idle waiting for
an event that would take more time to complete than the auto-suspend
timeout.

The auto-suspend cancellation is detected by the driver on the
host-side through a timeout for the processor to be idled, and is
simply rescheduled.

Change-Id: Ifdeeb80a632ac0145194d3c20f66256226e7efd4
Signed-off-by: Shahid Akhtar <sakhtar@ti.com>
Signed-off-by: Suman Anna <s-anna@ti.com>