x86/64: enable Hyper-V support in the x86_64 kernel config #628

Enabled Hyper-V network interface card driver, display adapter driver, storage driver, keyboard driver, mouse driver and Hyper-V utility and EFI boot support in the kernel for subtarget x86/64. Convert the img file to vhd by Ubuntu qemu-img, rather than by the buildroot's build-in qemu-img. Tested on Windows Server 2008 r2 and 2012 r2 Gen1 and Gen2 VMs.

Merged to nbd168 staging tree on Dec 20, 2016.

https://github.com/lede-project/source/pull/628