sh-pfc: r8a7790: Remove deprecated Ethernet MII/RMII pins

The pins have been removed from the datasheet, remove them here as well.
Signed-off-by: NShinya Kuribayashi <shinya.kuribayashi.px@renesas.com>
Signed-off-by: NLaurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>