net: ethernet: renesas: Add support for "Ethernet Switch"

Add initial support for Renesas "Ethernet Switch" device of R-Car S4-8.
The hardware has features about forwarding for an ethernet switch
device. But, for now, it acts as ethernet controllers so that any
forwarding offload features are not supported. So, any switchdev
header files and DSA framework are not used.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>