drm/i915/gvt: make dpcd_fix_data supports DP1.2

GVT-g will emulate a fixed DPCD data to VM for DP/eDP panel. Update
this data to latest DP1.2 with the maximum lane bandwidth of 5.4G/s
to support 4K resolution in VM.

V3: modify patch comment
V2: add inline comment to describe the dpcd_fix_data.

Signed-off-by: Pei Zhang <pei.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>