gvt-fixes-2018-04-03

- fix unhandled vfio ioctl return value (Gerd)
- no-op user interrupt for vGPU (Zhipeng)
- fix ggtt dma unmap (Changbin)
- fix warning in fb decoder (Xiong)
- dmabuf drm_format_mod fix (Tina)
- misc cleanup
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180403072835.kltk47gcwy7kuenv@zhen-hp.sh.intel.com