drm/i915/gvt: Init DPLL/DDI vreg for virtual display instead of inheritance.

drm/i915/gvt: Init DPLL/DDI vreg for virtual display instead of inheritance.

Init value of some display vregs rea inherited from host pregs. When
host display in different status, i.e. all monitors unpluged, different
display configurations, etc., GVT virtual display setup don't consistent
thus may lead to guest driver consider display goes malfunctional.

The added init vreg values are based on PRMs and fixed by calcuation
from current configuration (only PIPE_A) and the virtual EDID.

Fixes: c8fec534936a ("drm/i915/gvt: vGPU display virtualization")
Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Colin Xu <colin.xu@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200508060506.216250-1-colin.xu@intel.com