net: ipa: rearrange GSI structure fields

The dummy net_device is a large field in the GSI structure, but it
is not at all interesting from the perspective of debugging.  Move
it to the end of the GSI structure so the other fields are easier to
find in memory.

The channel and event ring arrays are also very large, so move them
near the end of the structure as well.

Swap the position of the result and completion fields to improve
structure packing.

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