i40e: Add helper for VF inited state check with timeout

Move the check for VF inited state (with optional up-to 300ms
timeout to separate helper i40e_check_vf_init_timeout() that
will be used in the following commit.

Tested-by: Ma Yuying <yuma@redhat.com>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>