xscale: Move the Intel XScale IXP drivers

Move the Intel XScale IXP drivers into drivers/net/ethernet/xscale/
and make the necessary Kconfig and Makefile changes.

CC: Krzysztof Halasa <khc@pm.waw.pl>
CC: Lennert Buytenhek <kernel@wantstofly.org>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>