ixgbe: enable relaxed ordering for SPARC

This patch makes sure that relaxed ordering is not disabled when
on SPARC, where it helps with performance.

CC: <kernel-team@fb.com>
CC: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Reported-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>