gve: make the completion and buffer ring size equal for DQO

gve: make the completion and buffer ring size equal for DQO

For the DQO queue format, the gve driver stores two ring sizes
for both TX and RX - one for completion queue ring and one for
data buffer ring. This is supposed to enable asymmetric sizes
for these two rings but that is not supported. Make both fields
reference the same single variable.

This change renders reading supported TX completion ring size
and RX buffer ring size for DQO from the device useless, so change
those fields to reserved and remove related code.

Reviewed-by: Praveen Kaligineedi <pkaligineedi@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Harshitha Ramamurthy <hramamurthy@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>