net/iavf: implement power management

net/iavf: implement power management

Implement support for the power management API by implementing a
`get_monitor_addr` function that will return an address of an RX ring's
status bit.

This patch is basically a cut-and-paste of the changes already
committed in ixgbe, i40e and ice drivers in 21.02. This extends
the availability of the power-saving mechanism to the iavf driver,
which is needed for those use-cases using virtual functions.

Patchset where PMD Power Management added in 21.02:
http://patchwork.dpdk.org/project/dpdk/list/?series=14756

Signed-off-by: David Hunt <david.hunt@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>