ice: Add more flexibility on how we assign an ITR index

This issue came about when looking at the VF function
ice_vc_cfg_irq_map_msg. Currently we are assigning the itr_setting value
to the itr_idx received from the AVF driver, which is not correct and is
not used for the VF flow anyway. Currently the only way we set the ITR
index for both the PF and VF driver is by hard coding ICE_TX_ITR or
ICE_RX_ITR for the ITR index on each q_vector.

To fix this, add the member itr_idx in struct ice_ring_container. This
can then be used to dynamically program the correct ITR index. This change
also affected the PF driver so make the necessary changes there as well.

Also, removed the itr_setting member in struct ice_ring because it is not
being used meaningfully and is going to be removed in a future patch that
includes dynamic ITR.

On another note, this will be useful moving forward if we decide to split
Rx/Tx rings on different q_vectors instead of sharing them as queue pairs.

Signed-off-by: Brett Creeley <brett.creeley@intel.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>