This patch adds support for RGMII protocol

NXP's LDPAA2 support RGMII protocol. LS1088A is the
first Soc supporting both RGMII and SGMII.

Signed-off-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
Signed-off-by: Amrita Kumari <amrita.kumari@nxp.com>
Signed-off-by: Ashish Kumar <Ashish.Kumar@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>