drm/i915/gvt: Fix vfio_edid issue for BXT/APL

BXT/APL has different isr/irr/hpd regs compared with other GEN9. If not
setting these regs bits correctly according to the emulated monitor
(currently a DP on PORT_B), although gvt still triggers a virtual HPD
event, the guest driver won't detect a valid HPD pulse thus no full
display detection will be executed to read the updated EDID.

With this patch, the vfio_edid is enabled again on BXT/APL, which is
previously disabled.

Fixes: 642403e3

 ("drm/i915/gvt: Temporarily disable vfio_edid for BXT/APL")
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/20201201060329.142375-1-colin.xu@intel.com
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>