drm/i915: fix issue in display pipe setup on IGDNG

During pipe DPMS off, instead of busy waiting pipe off, insert
delays during wait and don't loop after enough tries which matches
spec requirement. Also try to match DPMS on path by disable FDI TX
PLL in DPMS off. Disable PF by writing PF_WIN_SZ which really trigger
the update.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_reg.h

@@ -1848,6 +1848,8 @@
 #define PFA_CTL_1               0x68080
 #define PFB_CTL_1               0x68880
 #define  PF_ENABLE              (1<<31)
+#define PFA_WIN_SZ		0x68074
+#define PFB_WIN_SZ		0x68874
 
 /* legacy palette */
 #define LGC_PALETTE_A           0x4a000