device: Add GPU device support

Fixes kata-containers#542

Enable GPU device support in kata runtime, including GVT-g and GVT-d.
GVT-g: graphic virtualization technology with mediated pass through
GVT-d: graphic virtualization technology with direct pass through

BDF of device eg "0000:00:1c.0" is used to distinguish GPU device in GVT-d,
while sysfsdev of device eg "f79944e4-5a3d-11e8-99ce-479cbab002e4"is used
in GVT-g.

v2: split VFIO mediated device hotplug into standalone function.
    combine the acquisition of VFIO information into a function.
v3: correct the unit test function name.

Signed-off-by: Zhao Xinda <xinda.zhao@intel.com>

virtcontainers/device/drivers/vfio_test.go

@@ -12,7 +12,7 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestGetBDF(t *testing.T) {
+func TestGetVFIOInfo(t *testing.T) {
 	type testData struct {
 		deviceStr   string
 		expectedStr string