sh_eth: Remove obsolete r8a779x-ether platform_device_id entries

Since commit a483dcbf ("ARM: shmobile: lager: Remove legacy
board support"), R-Car Gen2 SoCs are only supported in generic DT-only
ARM multi-platform builds.  The driver doesn't need to match platform
devices by name anymore, hence remove the corresponding
platform_device_id entry.

Protect r8a779x_data by #ifdef CONFIG_OF as it's now referenced on DT
platforms only.

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