microblaze: Do not print eth device when DM_ETH is enabled

Doing the same fix as is done for ARM by:
"Avoid calling print_eths() with driver model"
(sha1: ff973800)

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>