macb: Move the Atmel driver

Move the Atmel driver into drivers/net/ethernet/cadence/ and
make the necessary Kconfig and Makefile changes.

CC: Nicolas Ferre <nicolas.ferre@atmel.com>
CC: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Jamie Iles <jamie@jamieiles.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>