drm/i915: Bump skl+ max plane width to 5k for linear/x-tiled

The officially validated plane width limit is 4k on skl+, however
we already had people using 5k displays before we started to enforce
the limit. Also it seems Windows allows 5k resolutions as well
(though not sure if they do it with one plane or two).

According to hw folks 5k should work with the possible
exception of the following features:
- Ytile (already limited to 4k)
- FP16 (already limited to 4k)
- render compression (already limited to 4k)
- KVMR sprite and cursor (don't care)
- horizontal panning (need to verify this)
- pipe and plane scaling (need to verify this)

So apart from last two items on that list we are already
fine. We should really verify what happens with those last
two items but I don't have a 5k display on hand atm so it'll
have to wait.

In the meantime let's just bump the limit back up to 5k since
several users have already been using it without apparent issues.
At least we'll be no worse off than we were prior to lowering
the limits.

Cc: stable@vger.kernel.org
Cc: Sean Paul <sean@poorly.run>
Cc: José Roberto de Souza <jose.souza@intel.com>
Tested-by: Leho Kraav <leho@kraav.com>
Fixes: 372b9ffb ("drm/i915: Fix skl+ max plane width")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111501


Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190905135044.2001-1-ville.syrjala@linux.intel.com


Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Sean Paul <sean@poorly.run>