When the number of potential color planes grew to 4 we stopped
setting all unused color plane offsets to ~0xfff. The code
still tries to do this, but actually does nothing since the
loop limits are bogus.

skl_check_main_surface() actually depends on this ~0xfff
behaviour as it will make sure to move the main surface
offset below the aux surface offset because the hardware
AUX_DIST must be a non-negative value [1], and for simplicity
it doesn't bother checking if the AUX plane is actually
needed or not. So currently it may end up shuffling the
main surface around based on some stale leftover AUX offset.

The skl+ plane code also just blindly calculates the AUX_DIST
whether or not the AUX plane is actually needed by the hw or
not, and that too will now potentially use some stale AUX
surface offset in the calculation. Would seem nicer to
guarantee a consistent non-negative AUX_DIST always.

So bring back the original ~0xfff offset behaviour for
unused color planes. Though it doesn't seem super likely
that this inconsistency would cause any real issues.

Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Fixes: 2dfbf9d2 ("drm/i915/tgl: Gen-12 display can decompress surfaces compressed by the media engine")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201008101608.8652-1-ville.syrjala@linux.intel.comReviewed-by: Imre Deak <imre.deak@intel.com>