Add phy-connection-type to gianfar nodes

The TSEC/eTSEC automatically detect their PHY interface type, unless
the type is RGMII-ID (RGMII with internal delay).  In that situation,
it just detects RGMII.  In order to fix this, we need to pass in rgmii-id
if that is the connection type.

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