sis*: Move the Silicon Integrated Systems (SiS) drivers

Move the SiS drivers into drivers/net/ethernet/sis/ and make the
necessary Kconfig and Makefile changes

CC: Daniele Venzano <venza@brownhat.org>
CC: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>