net: fman: Map the base address once

We don't need to remap the base address from the resource twice (once in
mac_probe() and again in set_fman_mac_params()). We still need the
resource to get the end address, but we can use a single function call
to get both at once.

While we're at it, use platform_get_mem_or_io and devm_request_resource
to map the resource. I think this is the more "correct" way to do things
here, since we use the pdev resource, instead of creating a new one.
It's still a bit tricky, since we need to ensure that the resource is a
child of the fman region when it gets requested.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Acked-by: Camelia Groza <camelia.groza@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>