net: stmmac: Add DWMAC glue layer for Renesas GBETH

Add the DWMAC glue layer for the GBETH IP found in the Renesas RZ/V2H(P)
SoC.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://patch.msgid.link/20250417084015.74154-4-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>