drm/i915/skl: Read the pipe WM HW state

This patch provides the implementation for reading the pipe wm HW
state.

v2: Incorporated Damien's review comments and also made modifications
    to incorporate the plane/cursor split.

v3: No need to ident a line that was fitting 80 chars
    Return early instead of indenting the remaining of a function
    (Damien)

v4: Rebase on top of nightly (minor conflict in intel_drv.h)
v5: Rebase on top of nightly (minor conflict in intel_drv.h)
v6: Rebase on top of nightly (minor conflict in intel_drv.h)

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Pradeep Bhat <pradeep.bhat@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 84f4f05..01bc558 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13266,7 +13266,9 @@
 		pll->on = false;
 	}
 
-	if (HAS_PCH_SPLIT(dev))
+	if (IS_GEN9(dev))
+		skl_wm_get_hw_state(dev);
+	else if (HAS_PCH_SPLIT(dev))
 		ilk_wm_get_hw_state(dev);
 
 	if (force_restore) {