ipg: Move the IC Plus driver

Move the IC Plus driver into drivers/net/ethernet/icplus/ and
make the necessary Kconfig and Makefile changes.

CC: <craig_rich@sundanceti.com>
CC: <sorbica@icplus.com.tw>
CC: <jesse@icplus.com.tw>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>