drm/i915/gvt: Set ENHANCED_FRAME_CAP bit

Specification says the bit7 of the DPCD MAX_LANE_COUNT (offset 0x02) must
be set to 1 when comes to the displayport version 1.2. This patch respects
the definition.

W/o this patch, guest i915 driver can only set the resolution to 1024*768,
and complains about the unsuccessful link training:

[    5.692193] i915 0000:00:02.0: [drm] *ERROR* index 0, lane_count 1 Link Training Unsuccessful

Fixes: e2e02cbb ("drm/i915/gvt: make dpcd_fix_data supports DP1.2")
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Tina Zhang <tina.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200921065807.247847-1-tina.zhang@intel.com

drivers/gpu/drm/i915/gvt/display.c

@@ -164,7 +164,7 @@ static unsigned char virtual_dp_monitor_edid[GVT_EDID_NUM][EDID_SIZE] = {
 
 /* let the virtual display supports DP1.2 */
 static u8 dpcd_fix_data[DPCD_HEADER_SIZE] = {
-	0x12, 0x014, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+	0x12, 0x014, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
 };
 
 static void emulate_monitor_status_change(struct intel_vgpu *vgpu)