drm/i915/gvt: Don't read ADPA_CRT_HOTPLUG_MONITOR from host

When host connects a crt screen, linux guest will detect two
screens: crt and dp. This is wrong as linux guest has only
one dp.

In order to avoid guest get host crt screen, we should set
ADPA_CRT_HOTPLUG_MONITOR to none. But MMIO_RO(PCH_ADPA) prevent
from that. So MMIO_DH should be used instead of MMIO_RO.

v2: Clear its staus to none at initialize, so guest don't
    get host crt.(Zhangyu)
v3: SKL doesn't have this register, limit it to pre_skl.(xiong)

Signed-off-by: Xiong Zhang <xiong.y.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

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

@@ -1905,7 +1905,7 @@ static int init_generic_mmio_info(struct intel_gvt *gvt)
 	MMIO_F(_PCH_DPD_AUX_CH_CTL, 6 * 4, 0, 0, 0, D_PRE_SKL, NULL,
 		dp_aux_ch_ctl_mmio_write);
 
-	MMIO_RO(PCH_ADPA, D_ALL, 0, ADPA_CRT_HOTPLUG_MONITOR_MASK, NULL, pch_adpa_mmio_write);
+	MMIO_DH(PCH_ADPA, D_PRE_SKL, NULL, pch_adpa_mmio_write);
 
 	MMIO_DH(_PCH_TRANSACONF, D_ALL, NULL, transconf_mmio_write);
 	MMIO_DH(_PCH_TRANSBCONF, D_ALL, NULL, transconf_mmio_write);