ar231x-eth: use dev_request_mem_region

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
ar531x: use preper way to registr eth driver

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
ar531x: add ram init

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>