net: netcp: use separate reg region for individual ethss modules

Ethss has multiple modules within the sub system
 - switch sub system
 - sgmii
 - mdio
 - switch module

NetCP driver re-uses existing davinci mdio driver. It requires to
have its own register region to map the reg space. So restructure
the code to use separate reg region for the individual modules it
manages. Use range property to define register space of NetCP and
use reg property to define individual reg spaces. So MDIO will have
its own reg space to map. This is a pre-requisite to enable MDIO
driver for NetCP.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: WingMan Kwok <w-kwok2@ti.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: Mugunthan V N <mugunthanvnm@ti.com>
CC: "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
CC: Grygorii Strashko <grygorii.strashko@ti.com>
CC: Christoph Jaeger <cj@linux.com>
CC: Lokesh Vutla <lokeshvutla@ti.com>
CC: Markus Pargmann <mpa@pengutronix.de>
CC: Kumar Gala <galak@codeaurora.org>
CC: Ian Campbell <ijc+devicetree@hellion.org.uk>
CC: Mark Rutland <mark.rutland@arm.com>
CC: Pawel Moll <pawel.moll@arm.com>
CC: Rob Herring <robh+dt@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>