net: ngbe: Add build support for ngbe

Add build options and guidance doc.
Initialize pci device access for Wangxun Gigabit Ethernet devices.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Mengyuan Lou <mengyuanlou@net-swift.com>
Link: https://lore.kernel.org/r/20220826034609.51854-1-mengyuanlou@net-swift.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>