net: ipa: add a transaction committed list

We currently put a transaction on the pending list when it has
been committed.  But until the channel's doorbell rings, these
transactions aren't actually "owned" by the hardware yet.

Add a new "committed" state (and list), to represent transactions
that have been committed but not yet sent to hardware.  Define
"pending" to mean committed transactions that have been sent
to hardware but have not yet completed.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>