ARM: orion: Register DSA switch as a MDIO device

Utilize the ability to pass board specific MDIO bus information towards a
particular MDIO device thus allowing us to provide the per-port switch layout
to the Marvell 88E6XXX switch driver.

Since we would end-up with conflicting registration paths, do not register the
"dsa" platform device anymore.

Note that the MDIO devices registered by code in net/dsa/dsa2.c does not
parse a dsa_platform_data, but directly take a dsa_chip_data (specific
to a single switch chip), so we update the different call sites to pass
this structure down to orion_ge00_switch_init().

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>