net: stmmac: dwmac-starfive: Add support for JH7100 SoC

Add a missing quirk to enable support for the StarFive JH7100 SoC.

Additionally, for greater flexibility in operation, allow using the
rgmii-rxid and rgmii-txid phy modes.

Co-developed-by: Emil Renner Berthing <kernel@esmil.dk>
Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>