SPM: Add Asynchronous code to ns_agent_mailbox

Add AGENT_STATUS_IN_PROGRESS and ASYNC_MSG_REPLY defines.
Add handling of ASYNC_MSG_REPLY to ns_agent_mailbox main loop.
For now at least, this will never be called, this is simply to establish
the new API.

No behavioural change.

Change-Id: Iaee07d6eac097a20bf807844741cbecc54ad6ffd
Signed-off-by: Chris Brand <chris.brand@cypress.com>
4 files changed