cassini/niu/sun*: Move the Sun drivers

Moves the Sun drivers into drivers/net/ethernet/sun/ and make
the necessary Kconfig and Makefile changes.

Oliver Hartkopp <socketcan@hartkopp.net> suggested removing the
sun* prefix on the driver names.  This type of change I will
leave up to the driver maintainers.

CC: Sam Creasey <sammy@sammy.net>
CC: Adrian Sun <asun@darksunrising.com>
CC: Benjamin Herrenscmidt <benh@kernel.crashing.org>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>