An event ring's state only needs to be known when it is allocated,
reset, or deallocated.  We check an event ring's state both before
and after performing an event ring control command that changes
its state.  These are only issued at startup and shutdown, so there
is very little value in caching the state.

Stop recording a copy of the channel's last known state, and instead
fetch the true state from hardware whenever it's needed.  In such
cases, *do* record the state in a local variable, in case an error
message reports it (so the value reported is the value seen).
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>