net: macb: Convert to driver model

Add driver-model support to this driver. The old code remains for now so
that we can convert boards one at a time.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
Tested-on: smartweb, corvus, taurus, axm
Tested-by: Heiko Schocher <hs@denx.de>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Andreas Bießmann <andreas@biessmann.org>