net/mlx5: optimize counter extend memory

net/mlx5: optimize counter extend memory

Counter extend memory was allocated for non-batch counter to save the
extra DevX object. Currently, for non-batch counter which does not
support aging, entry in the generic counter struct is used only when
counter is free in free list, and bytes in the struct is used only when
counter is allocated in using.

In this case, the DevX object can be saved to the generic counter struct
union with entry memory when counter is allocated and union with bytes
when counter is free.
And pool type is also not needed as non-fallback mode only has generic
counter and aging counter, just a bit to indicate the pool is aged or
not will be enough.

This eliminates the counter extend info struct saves the memory.

Signed-off-by: Suanming Mou <suanmingm@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>