net: hns3: Add HNS3 driver to kernel build framework & MAINTAINERS

This patch updates the MAINTAINERS file with HNS3 Ethernet driver
maintainers names and other details. This also introduces the new
Makefiles required to build the HNS3 Ethernet driver and updates
the existing Kconfig file in the hisilicon folder.

Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>