net: ixp4xx_hss: Convert to use DT probing

IXP4xx is being migrated to device tree only. Convert this
driver to use device tree probing.

Pull in all the boardfile code from the one boardfile and
make it local, pull all the boardfile parameters from the
device tree instead of the board file.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>