Microsoft Azure Network Adapter(MANA) VF support

MANA is the new network adapter from Microsoft which will be available
in Azure public cloud. It provides SRIOV NIC as virtual function to
guest OS running on Hyper-V.

The code can be divided into two major parts. Gdma_main.c is the one to
bring up the hardware board and drives all underlying hardware queue
infrastructure. Mana_en.c contains all main ethernet driver code.
It has only tested and supported on amd64 architecture.

PR: 256336
Reviewed by: decui@microsoft.com
Tested by: whu
MFC after: 2 week
Relnotes: yes
Sponsored by: Microsoft
Differential Revision: https://reviews.freebsd.org/D31150