Extend qemux86-64 images to support real hardware

Extend qemux86-64 images to support real hardware

* Build wic images for qemux86-64 which can be written to a USB stick or
  SD card.

* Support both virtual and physical displays for all qemu targets.

* Use a wks file which works on both virtual and physical machines. EFI
  is now required to boot the VMDK image.

* Drop inclusion of `microcode.cpio` in the boot partition in the wic
  file `systemd-intel-corei7-64-bootdisk.wks`. This file is not
  available for qemux86-64 images and is not strictly necessary.

Bug-AGL: SPEC-2931

Change-Id: Ib3982906e52d3a964a921c9a2234cab697fe0551
Signed-off-by: Paul Barker <pbarker@konsulko.com>