net: sh_eth: implement R-Car Gen[12] fallback compatibility strings

Implement fallback compatibility strings for R-Car Gen 1 and 2.

In the case of Renesas R-Car hardware we know that there are generations of
SoCs, f.e. Gen 1 and 2. But beyond that its not clear what the relationship
between IP blocks might be. For example, I believe that r8a7790 is older
than r8a7791 but that doesn't imply that the latter is a descendant of the
former or vice versa.

We can, however, by examining the documentation and behaviour of the
hardware at run-time observe that the current driver implementation appears
to be compatible with the IP blocks on SoCs within a given generation.

For the above reasons and convenience when enabling new SoCs a
per-generation fallback compatibility string scheme is being adopted for
drivers for Renesas SoCs.

Note that R-Car Gen2 and RZ/G1 have many compatible IP blocks.  The
approach that has been consistently taken for other IP blocks is to name
common code, compatibility strings and so on after R-Car Gen2.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/renesas/sh_eth.c

@@ -3095,6 +3095,8 @@ static const struct of_device_id sh_eth_match_table[] = {
 	{ .compatible = "renesas,ether-r8a7793", .data = &rcar_gen2_data },
 	{ .compatible = "renesas,ether-r8a7794", .data = &rcar_gen2_data },
 	{ .compatible = "renesas,ether-r7s72100", .data = &r7s72100_data },
+	{ .compatible = "renesas,rcar-gen1-ether", .data = &rcar_gen1_data },
+	{ .compatible = "renesas,rcar-gen2-ether", .data = &rcar_gen2_data },
 	{ }
 };
 MODULE_DEVICE_TABLE(of, sh_eth_match_table);