net/bnxt: require async completion ring for vector path

net/bnxt: require async completion ring for vector path

Disable support for vector mode when async completions can be placed
in a receive completion ring and change the default for all platforms
to use a dedicated async completion ring.

Simplify completion handling in vector mode receive paths now that
it no longer needs to handle async completions.

Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Signed-off-by: Lance Richardson <lance.richardson@broadcom.com>