drm/i915: Add WA for planes ending close to left screen edge

drm/i915: Add WA for planes ending close to left screen edge

While running the kms_plane clipping test I noticed a similar problem to
the one described in Display WA #1175. In this case, similarly for
planes other than the cursor, with 1 or 3 pixels visible from the left
edge of the screen to the end of the plane and an odd plane X offset
used for clipping causes the same kind of underflow and display
corruption as described for WA #1175. Fix this in a similar way as that
WA rejecting planes ending <4 pixels from the left screen edge.

v2:
- Rebase on v2 of patch 1/1.

Testcase: igt/kms_plane/plane-clipping-pipe-*-planes
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180116112415.22060-2-imre.deak@intel.com