i40e: Introduce and use macros for iterating VSIs and VEBs

Introduce i40e_for_each_vsi() and i40e_for_each_veb() helper
macros and use them to iterate relevant arrays.

Replace pattern:
for (i = 0; i < pf->num_alloc_vsi; i++)
by:
i40e_for_each_vsi(pf, i, vsi)

and pattern:
for (i = 0; i < I40E_MAX_VEB; i++)
by
i40e_for_each_veb(pf, i, veb)

These macros also check if array item pf->vsi[i] or pf->veb[i]
are not NULL and skip such items so we can remove redundant
checks from loop bodies.

Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>