net: ethernet: ave: Add capability of rgmii-id mode

This allows you to specify the type of rgmii-id that will enable phy
internal delay in ethernet phy-mode.

This adds all RGMII cases to all of get_pinmode() except LD11, because LD11
SoC doesn't support RGMII due to the constraint of the hardware. When RGMII
phy mode is specified in the devicetree for LD11, the driver will abort
with an error.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: David S. Miller <davem@davemloft.net>