A given AMP configuration for a board may make either one, or neither
of, the ethernet ports available to U-Boot. The Icicle's init code will
fail if mac1 is not present, so move it to the optional approach taken
for mac0.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>