com20020_cs: Move the PCMCIA Arcnet driver

Move the COM20020 PCMICA Arcnet driver into drivers/net/arcnet/ with
the other Arcnet drivers.  Made the necessary Kconfig and Makefile
changes as well.

Since this was the "last" PCMCIA driver in drivers/net/pcmcia/, this patch
also cleans up the references to drivers/net/pcmcia.

CC: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>