net/fm: fixup ethernet for mEMAC

- set proper compatible property name for mEMAC.
- fixed ft_fixup_port for dual-role mEMAC, which will lead to
  MAC node disabled incorrectly.

Signed-off-by: Shengzhou Liu <Shengzhou.Liu@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>